The Fourth Amendment and the Third-Party Doctrine
The government can obtain enormous amounts of information about a person from third parties—banks, telephone companies, internet service providers, email providers, and technology companies.
Does the Fourth Amendment require investigators to obtain a search warrant before acquiring that information?
The answer depends on what information the government seeks, how it was generated, how much it reveals about the person, and the circumstances under which it was provided to the third party.
The traditional third-party doctrine generally provides that a person loses a reasonable expectation of privacy in information voluntarily disclosed to another person or company. But the Supreme Court’s decision in Carpenter v. United States established an important limitation on the mechanical application of that doctrine to modern digital information.
Federal criminal defense attorney Michael J. Petro has more than 35 years of criminal defense experience representing individuals in cases involving search warrants, electronic evidence, computers, cell phones, internet activity, and alleged Fourth Amendment violations.
What Is the Third-Party Doctrine?
The Fourth Amendment protects people against unreasonable searches and seizures by the government.
Ordinarily, a Fourth Amendment issue arises when the government intrudes upon an area in which a person has a constitutionally protected expectation of privacy.
The third-party doctrine developed from Supreme Court decisions holding that certain information voluntarily provided to another person or business does not carry the same Fourth Amendment protection.
The two traditional Supreme Court cases are:
These decisions became the foundation for decades of cases involving government access to third-party information.
United States v. Miller and Bank Records
In United States v. Miller, federal investigators obtained the defendant’s bank records through subpoenas.
Miller argued that the government’s acquisition of his financial records violated the Fourth Amendment.
The Supreme Court rejected the argument.
The Court reasoned, in part, that the records were the banks’ business records and contained information that Miller had voluntarily conveyed to them in the ordinary course of business.
As a result, Miller could not assert a protected Fourth Amendment expectation of privacy in those bank records.
Miller became one of the principal foundations of the third-party doctrine.
Smith v. Maryland and Telephone Numbers
Three years later, the Supreme Court decided Smith v. Maryland.
Police had a telephone company install a pen register to record the telephone numbers dialed from the defendant’s home telephone.
The Supreme Court held that the installation and use of the pen register was not a Fourth Amendment search.
The Court reasoned that telephone users necessarily convey dialed telephone numbers to the telephone company so the calls can be completed.
Together, Miller and Smith established the traditional proposition that information voluntarily conveyed to a third party may lose Fourth Amendment protection.
The Third-Party Doctrine Meets the Internet
The development of the internet created questions the Supreme Court could not have anticipated when it decided Miller in 1976 and Smith in 1979.
Modern internet activity can generate extensive information held by third parties, including:
- IP addresses
- Email account information
- Login records
- Location information
- Search activity
- Cloud data
- Subscriber information
- Telephone records
- Financial information
- Application data
- Website activity
Applying a rule developed around bank records and dialed telephone numbers to modern digital information can raise difficult Fourth Amendment questions.
One important Seventh Circuit case involving this issue is United States v. Caira, 833 F.3d 803 (7th Cir. 2016).
United States v. Caira
Caira began with an investigation into an attempt to purchase sassafras oil, a chemical that can be used in manufacturing MDMA, commonly known as ecstasy.
Someone using the email address gslabs@hotmail.com contacted a Vietnamese website seeking to purchase the chemical.
The Drug Enforcement Administration was monitoring the website.
Investigators needed to determine who was behind the Hotmail account.
The DEA used administrative subpoenas to obtain information from technology companies rather than first obtaining a search warrant.
That information helped investigators identify Frank Caira.
Caira Challenged the Government’s Acquisition of His IP Address
Caira moved to suppress evidence.
He argued that the government’s acquisition of information concerning the IP addresses used to access his Hotmail account constituted a Fourth Amendment search and therefore required a warrant.
Caira’s argument had an intuitive basis.
An IP address can provide information that connects internet activity to a physical location.
Caira argued that people have a reasonable expectation of privacy in their physical location and that obtaining his IP address information implicated that privacy interest.
The Seventh Circuit rejected the argument under the third-party doctrine.
Why the Seventh Circuit Rejected Caira’s Argument
The Seventh Circuit concluded that Caira had shared his IP address with Microsoft when he logged into his Hotmail account.
Microsoft needed the IP address to send information back to the computer from which Caira was accessing his email.
The court therefore applied Miller and Smith.
Because Caira voluntarily transmitted the IP address information to Microsoft, the court held that he did not have a reasonable expectation of privacy in that information.
Accordingly, the DEA’s acquisition of the IP address information did not constitute a Fourth Amendment search, and a search warrant was not required.
Then the Supreme Court Decided Carpenter v. United States
Two years after Caira, the Supreme Court decided one of the most important modern Fourth Amendment cases involving digital information:
Carpenter v. United States, 585 U.S. 296 (2018).
The government had obtained historical cell-site location information from Carpenter’s wireless carriers.
Those records provided extensive information about the location and movements of Carpenter’s cell phone over an extended period.
Under a straightforward application of the traditional third-party doctrine, the government argued that Carpenter had no reasonable expectation of privacy because the information was held by his wireless carriers.
The Supreme Court disagreed.
Carpenter Limited the Traditional Third-Party Doctrine
The Supreme Court held that the government’s acquisition of Carpenter’s historical cell-site location records constituted a Fourth Amendment search.
The Court recognized the traditional third-party doctrine established by Miller and Smith, but declined to mechanically extend it to the detailed location information generated by modern cell phones.
The Court emphasized the unique nature of cell-site location information.
Cell phones accompany people throughout their daily lives and continuously generate location information through interactions with cell towers.
The resulting records can provide the government with a detailed chronicle of a person’s physical movements.
The Supreme Court therefore concluded that Carpenter maintained a legitimate expectation of privacy in the historical cell-site location information at issue despite the fact that the records were held by third-party wireless carriers.
Carpenter Did Not Eliminate the Third-Party Doctrine
This distinction is important.
Carpenter did not overrule Miller or Smith.
The Supreme Court expressly recognized the continued existence of the traditional third-party doctrine.
Instead, the Court held that the doctrine did not automatically control the fundamentally different circumstances presented by extensive historical cell-site location information.
The result is a more nuanced Fourth Amendment analysis.
The fact that information is held by a third-party company remains important—but it does not necessarily end the constitutional inquiry in every digital-evidence case.
What Does Carpenter Mean for Caira and IP Addresses?
Caira and Carpenter involve related but different types of digital information.
Caira involved IP addresses transmitted to Microsoft when the defendant accessed his Hotmail account.
Carpenter involved an extensive historical record of cell-site location information that could reveal a person’s movements over time.
The Seventh Circuit held in Caira that the defendant had no reasonable expectation of privacy in the IP-address information he voluntarily transmitted to Microsoft.
Carpenter later demonstrated, however, that courts should not assume every category of information held by a technology company automatically falls outside the Fourth Amendment merely because a third party possesses it.
The nature and revealing quality of the information matter.
IP Addresses and Fourth Amendment Privacy
An IP address is not the same thing as historical cell-site location information.
An IP address may identify or help identify the internet connection associated with particular online activity.
Investigators may use IP address information to:
- Identify an internet service provider
- Obtain subscriber information
- Connect online activity to an internet account
- Identify a residence
- Connect activity to an email account
- Support an application for a search warrant
- Develop additional investigative leads
But an IP address does not necessarily identify the individual who engaged in the activity.
Several people may use the same internet connection, and numerous devices may operate through the same network.
The distinction between identifying an internet connection and identifying the person responsible for the activity can become important in a criminal case.
Information Held by Technology Companies
Modern criminal investigations frequently involve information maintained by companies such as:
- Microsoft
- Apple
- Meta
- Internet service providers
- Cellular carriers
- Cloud-storage providers
- Financial institutions
- Social-media platforms
The government may seek this information through different legal processes depending on the type of data involved.
Those methods can include:
- Subpoenas
- Court orders
- Search warrants
- Statutory disclosure procedures
- Consent
- Emergency disclosure requests
The fact that a company possesses information does not, by itself, determine whether the Fourth Amendment requires a warrant.
The type of information and governing law must be examined.
Subscriber Information Is Different From Content
Another important distinction is between subscriber information and communication content.
Basic subscriber information might include identifying information associated with an account.
Content may include the actual substance of emails, messages, photographs, stored documents, or other communications.
Different categories of information can receive different legal protection.
A subpoena sufficient to obtain one category of records may not necessarily authorize the government to obtain the contents of private communications.
Defense counsel should therefore determine exactly what information the government acquired and what legal process was used to obtain it.
Location Information Receives Special Attention
Location information presents particularly significant privacy concerns because it can reveal where a person travels, spends time, sleeps, works, worships, receives medical treatment, and associates with others.
Carpenter recognized that prolonged historical cell-site information can reveal an extensive record of a person’s physical movements.
The Supreme Court emphasized that the government’s acquisition of that type of information was qualitatively different from the relatively limited business records involved in Miller and Smith.
That reasoning has become an important part of modern Fourth Amendment litigation involving digital technology.
The Third-Party Doctrine Is Not a Simple Rule for Digital Evidence
It is tempting to state the doctrine this way:
Give information to a third party, and you lose all Fourth Amendment protection.
After Carpenter, that statement is too broad.
A modern analysis may require asking:
- What information did the government obtain?
- How revealing is that information?
- How much information was collected?
- Over what period of time?
- Was disclosure to the third party genuinely voluntary?
- Was the information automatically generated by technology?
- Does the information reveal physical movements?
- Does it expose intimate details of a person’s life?
- What legal process did the government use?
- Did investigators obtain a warrant?
- Was a warrant constitutionally required?
The answers can determine whether government acquisition of third-party data constitutes a Fourth Amendment search.
Third-Party Records Can Lead to a Search Warrant
Even when investigators can lawfully obtain particular third-party records without a warrant, those records may later be used to establish probable cause for a much more intrusive search.
For example, investigators might obtain:
- Subscriber information associated with an internet account
- IP address information associated with online activity
- Information identifying a residence
- Additional investigative evidence
- A search warrant for the residence and electronic devices
The defense should examine each step.
The fact that the final search was conducted pursuant to a warrant does not necessarily preclude the examination of the evidence and representations used to obtain the warrant.
Challenging Digital Evidence
A Fourth Amendment challenge involving third-party information can require careful analysis of both constitutional law and technology.
Potential issues include:
- Whether the defendant had a reasonable expectation of privacy
- Whether the information was voluntarily disclosed
- Whether Carpenter applies
- Whether a warrant was required
- Whether the government complied with applicable statutes
- Whether the warrant affidavit established probable cause
- Whether the information in the affidavit was false or misleading
- Whether investigators omitted material information
- Whether the warrant was sufficiently particular
- Whether investigators exceeded the authorized scope of the search
When appropriate, these issues may be litigated through a motion to suppress evidence.
Digital Privacy and the Fourth Amendment Continue to Develop
The third-party doctrine originated in an era of paper bank records and landline telephones.
Today’s criminal investigations can involve enormous quantities of information automatically generated and stored by computers, cell phones, internet providers, applications, and cloud services.
Carpenter recognized that applying decades-old Fourth Amendment rules to modern technology requires attention to the nature of the information the government obtains.
The fundamental question remains whether the government’s conduct invaded an expectation of privacy protected by the Fourth Amendment.
Experienced Federal Search and Seizure Attorney
Michael J. Petro has more than 35 years of criminal defense experience representing individuals facing serious state and federal criminal investigations and prosecutions.
Digital evidence can play a central role in federal criminal cases involving fraud, drugs, firearms, child sexual abuse material, and other alleged offenses.
When the government obtains information from a third party, the defense should determine precisely what information was acquired, how investigators obtained it, whether a warrant was required, and how that information was subsequently used.
Caira demonstrates the traditional application of the third-party doctrine to IP address information. Carpenter demonstrates that the doctrine has constitutional limits when modern technology permits the government to obtain particularly revealing information about a person’s life and movements.
If you are facing a criminal investigation involving electronic records, IP addresses, cell phone data, location information, or another digital search, contact federal criminal defense attorney Michael J. Petro to discuss your case.