A 21-year old man accused of killing three Japanese tourists in a stabbing rampage in Guam earlier this month has pleaded not guilty to aggravated murder and other charges by reason of insanity.

The Superior Court of Guam accepted Chad Ryan DeSoto’s plea during a hearing on Wednesday, a spokeswoman for the Guam attorney general’s office said.

Superior Court Magistrate Judge Alberto Tolentino immediately ordered a psychiatric evaluation to determine whether DeSoto is mentally competent to be held responsible for the crime, reports The Associated Press.

A follow-up hearing, at which a jury of 12 citizens will decide whether he can be held accountable for the charges, was set for March 20, according to local judicial authorities.

DeSoto faces life imprisonment without parole if convicted, sources said, adding that he may still change his mind to admit the charges and appeal the sentence.

Three Japanese tourists were killed after DeSoto allegedly crashed his car onto a sidewalk and struck seven tourists in a major tourist district in the US territory. Another 11 people were injured in the incident.