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Compelling a fingerprint to unlock cell phone wasn't "self-incrimination"

When M.H. returned home after running errands, she saw that the attached garage's entry door had been kicked in. A burglar had stolen a safe, a laptop, and several items of jewelry. M.H. found an envelope in her driveway that had the name of S.W. written on it. Officers photographed and measured the shoe prints on the door.

An investigator tracked down the model and license plate number of a car registered to S.W. The investigator learned that S.W. had pawned several pieces of jewelry. M.H. identified the pawned jewelry as stolen from her home. When police located S.W.'s car, Diamond was driving it. They arrested Diamond an unrelated outstanding warrant. He was booked into jail and his shoes and cellphone were booked into property.

The investigator saw that Diamond's shoe tread appeared to be the same as the tread prints left on M.H.'s damaged door. The investigator obtained a search warrant for Diamond's property, including his cell phone. However, the phone was locked and required a fingerprint to open it. Diamond refused to provide a fingerprint to unlock his mobile phone.

The prosecution asked the court to compel Diamond to provide his fingerprint and unlock the phone. Diamond argued that forcing him to provide his fingerprint to unlock the cellphone would violate his Fifth Amendment privilege against compelled self-incrimination. After the court ordered Diamond to provide his fingerprint, he still refused. Finally, under threat of a criminal contempt charge, Diamond cooperated. Police extracted inculpatory text messages between Diamond and S.W. A jury convicted Diamond of burglary. Diamond appealed, arguing that he was forced to incriminate himself by providing the fingerprint to unlock the phone.

No other appellate court had yet considered whether the act of providing a biometric identifier, such as a fingerprint, to unlock a device constituted an act of self-incrimination. The Minnesota Supreme Court held that no Fifth Amendment violation occurred. The court compared providing a fingerprint to taking a blood sample, appearing in an identification lineup or providing a handwriting or voice exemplar. The U.S. Supreme Court has held that there is no testimonial self-incrimination when a person is compelled to provide "real or physical evidence" that is "used solely to measure … physical properties," United States v. Dionisio, 410 U.S. 1 (1973), or to "exhibit … physical characteristics." United States v. Wade, 388 U.S. 218 (1967).

The Minnesota Supreme Court said that ordering Diamond to provide his "fingerprint for the fingerprint's physical characteristics and not for any implicit testimony from the act of providing the fingerprint" was not an incriminating testimonial communication. "Moreover, the fingerprint was physical evidence from Diamond's body, not evidence of his mind's thought processes." However, the court noted that it was not equating act of compulsion to provide a fingerprint to compulsion to reveal a password, leaving that question for another day. State v. Diamond, 2018 WL 443356 (Minn. 2018).