Does a Fingerprint Unlocking a Cell Phone Mean Self-Incrimination?

State v. Diamond, (Minn. 2018)

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. Additionally, M.H. found an envelope in her driveway that had the name of S.W. written on it, and officers photographed and measured the shoeprints left on the kicked-in 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 and M.H. identified the pawned jewelry as stolen from her home. When police located S.W.’s car, Matthew Diamond was driving it. They arrested Diamond on an unrelated outstanding warrant. Diamond was booked into jail and his shoes and cell phone 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, so he obtained a search warrant for Diamond’s property, including his cell phone. However, the phone was locked and required a fingerprint to open it, which Diamond refused to provide.

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 cell phone 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., and 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 it was not equating the act of compulsion to provide a fingerprint to compulsion to reveal a password, leaving that question for another day.

Ken Wallentine

KEN WALLENTINE is the Chief of the West Jordan (Utah) Police Department and former Chief of Law Enforcement for the Utah Attorney General. He has served over four decades in public safety, is a legal expert and editor of Xiphos, a monthly national criminal procedure newsletter. He is a member of the Board of Directors of the Institute for the Prevention of In-Custody Death and serves as a use of force consultant in state and federal criminal and civil litigation across the nation.

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