If that is the case then there should be no problem convicting him.

In a filesharing seneario it is common for feds to see what you got before the raid that grabs the physical drive.

https://en.wikipedia.org/wiki/Giles_Corey

The law is actually that physical features/etc can be compelled because they are not testimonial.

“[i]t is compulsion of the accused to exhibit his physical characteristics, not compulsion to disclose any knowledge he might have.”

United States v. Wade

"“the task that Diamond was compelled to perform—to provide his fingerprint—is no more testimonial than furnishing a blood sample, providing handwriting or voice exemplars, standing in a lineup, or wearing particular clothing.”"

State v. Diamond (This is a state case but applying the federal constitution).

Note also that fingerprints are almost always taken at booking, etc. They just aren't transferable in a way that lets the police use them to unlock the phone.

Passcodes, on the other hand are often testimonial. Entering the combination to a safe proves you probably had ownership/control of the safe, for example.

In those situations, generally the government has to be able to prove that you own it. If they can, you will be forced to open the safe.

In the case of phones, the only interesting intermediate cases are phones where ownership can't be proven easily by other evidence.

(Note:I don't necessarily agree with these doctrines, but that is the current law)

Is this not also true for face/fingerprint ID? Proving the face/fingerprint ID proves you probably had ownership control of the device.

We treat biometrics like a secret (i.e. password), but really it's not much better than public information (i.e. username).

:I