Suppose a police officer knocks on your door and tells you there was a robbery in the neighborhood and asks if he can ask you some questions about it, but really what he wants is to collect evidence against you for an entirely different case.

You invite the officer into your house and answer his questions. Suppose there’s a drinking glass of yours in plain sight on the table. What he really wants is a sample of your DNA, so when you're not looking, he takes the glass.

Can the officer (or, more likely, lawyers for the prosecution) argue that this seizure was legal because you did invite the officer into the house (believing it to be for another reason)?

  • SCOTUS has ruled that police can take your DNA following any arrest, so they'd probably have an easier time doing it that way. (Police planting evidence is pretty hard to prove, unless it's a pattern.)
    – Fizz
    Oct 6, 2021 at 4:49

3 Answers 3


First, welcome to LSE, Josh. And congratulations on such a nice first question.

The answer to your question is No.

Inviting an officer into your house to talk about a robbery does not give the officer the right to search your house. Talking and searching involve two different amendments, and you must waive your rights under each explicitly. However, under the plain view doctrine, police who are lawfully in your house can search (and seize) your property without a warrant if:

a) the stuff they search or seize is in plain view (ie, “immediately apparent”); and,

b) they have probable cause to believe that whatever is in plain view contains evidence of a crime. (In other words, they can only search without a warrant if they could get a warrant, based on what is in plain view.)

In your hypothetical, the police do not meet all of the requirements for a warrantless search under the plain view doctrine. They are there legally, and the glass is in plain view. However, the DNA is not in plain view, which means they will need to search the glass to find it. To search the glass, they need probable cause to believe that your DNA will link you to a crime.

In this case, the need for probable cause creates a catch-22 for the police. Because they can't get probable cause merely from looking at the glass, the police must have had probable cause to get your DNA before walked in your door. But if they had probable cause before they showed up, then the 4th Amendment requires them to get a warrant. The plain view rule does not allow the police to skip the warrant requirement for their own convenience.

To see how seizing the glass would require probable cause, consider Arizona v. Hicks. In Hicks, police entered an apartment looking for a shooter. After finding the shooter, the police saw expensive stereo equipment that “seemed out of place in the squalid and otherwise ill-appointed four-room apartment.” Suspicious, they moved the stereo so they could read the serial number. When it turned out the stereo was stolen, they charged Hicks with theft. On appeal, the Court held that the serial number was not in plain view, and that seeming “out of place” did not establish probable cause to search the stereo. As a result, the search was unconstitutional.

  • 1
    Thanks for the welcome and detailed answer! Not that the law is really about common sense, but this does make a lot of sense to me. Jul 2, 2020 at 14:17

Yes and No

See Katz v. United States, 389 U.S. 347, 351 (1967):

What a person knowingly exposes to the public, even in his home or office, is not a subject of Fourth Amendment protection. But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.

The glass has clearly been "knowingly exposed" and if that glass was, on the normal methods of examination by the officer (sight, smell etc.), evidence of a crime then it would be able to be used as evidence. However, any DNA on that glass is not "knowingly exposed" - finding the DNA requires a laboratory, specialised equipment and trained technicians.

  • 1
    It sounds like the issue is less about what you know to be exposed than it is about "normal methods of examination", that is, what human senses can reasonably detect based only on inspection and what sorts of things are relevant to a specific crime. So if there's been a murder and there's a known possession of the victim sitting on the table, a police officer can act on it. But a drinking glass by itself doesn't indicate a crime in any way, and only does so if the officer takes it for offsite analysis. So is the answer for the drinking glass situation a hard No? Jun 17, 2020 at 12:19

Hard to Tell

The individual consented to a search by letting the officer come in, and consent searches are held to be reasonable. Katz was an unconsented invasion of privacy (picking up sound through the glass in a telelphone booth). The glass has been "knowingly exposed", and the glass is in plain sight (Horton v. California, 496 U.S. 128. "The Fourth Amendment does not prohibit the warrantless seizure of evidence in plain view"). One condition attaching to such seizures is that "the officer must have a lawful right of access to the object itself", which derives from the consent. The other condition is that "the object's incriminating character must be 'immediately apparent'". This later conclusion derives from Coolidge v. New Hampshire, 403 U.S. 443 which finds that "the extension of the original justification is legitimate only where it is immediately apparent to the police that they have evidence before them".

Is it immediately apparent that a glass constitutes evidence? It is hard to imagine that DNA on a glass is itself evidence of a crime. DNA from a glass could provide the probable cause (given a match with crime-scene DNA) for a court-ordered collection of DNA from the person, and that DNA could be matched with the DNA found at the crime. But DNA from a glass in a house conjectured to be the DNA of the owner is not an admissible substitute for directly-collected evidence.

Is extraction of DNA itself a search? In some cases it is, see Maryland v King, where the court finds that

using a buccal swab on the inner tissues of a person’s cheek in order to obtain DNA samples is a search

with related citations. However, in some circumstances, such a body search is deemed reasonable, especially when the state needs to identify an individual under arrest (King). Things discarded in the trash may also be a search yet be permitted (California v. Greenwood, 486 U.S. 35), when the expectation of privacy is not reasonable.

In a current case (SD v. Bentaas), defense via amici is urging that all DNA analysis constitutes a search, subject to Fourth Amendment protections. The argument that DNA contains vast amounts of personal information, and

the extraction of an individual’s DNA sample and “the creation of his DNA profile constitute[] a search for Fourth Amendment purposes.” United States v. Davis, 690 F.3d 226

Amici also urge that the state has "seized and has access to all of Ms. Bentaas’s genetic information as a result of the underlying DNA extraction". This case has the potential to have a substantial impact on DNA and the Fourth Amendment.

  • "DNA from a glass in a house conjectured to be the DNA of the owner is not an admissible substitute for directly-collected evidence." Does it matter if this is not actually a conjecture because the officer saw the owner drinking from the glass and KNOWS that the DNA is that of the owner? Jun 18, 2020 at 14:29
  • Also, if you have just been drinking from the glass "it is immediately apparent to the police that they have evidence before them", if "evidence" means that it has your DNA on it. But it is NOT immediately apparent that this DNA will in fact connect you to the crime. So in this scenario, it sounds like the sight of an ordinary drinking glass doesn't meet the Coolidge requirements. Is that right? Jun 18, 2020 at 14:31
  • Also, wow, thanks for the incredibly detailed answer! Jun 18, 2020 at 14:31
  • Update: Apparently the case alluded to at the end of the answer had the judge rule that the DNA was admissible, though the trial itself has yet to be concluded.
    – Nat
    Oct 6, 2021 at 1:59

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