FORT LAUDERDALE, Fla. – A 19-year-old Florida State University student with no criminal record fatally stabbed a couple at random outside their house, wounded their neighbor and was biting the dead man’s face when deputies finally subdued him, authorities said Tuesday.

Austin Harrouff may have been on hallucinogenic drugs when he attacked Michelle Mishcon, 53, and John Stevens, 59, outside their home in Tequesta, Martin County Sheriff William Snyder said.

The sheriff said Harrouff had joined his family for dinner when he stormed off, apparently agitated about slow service. His parents were so worried by his behavior that they called police and some of his fraternity brothers in an attempt to find him.

About 45 minutes later, he apparently targeted the couple at random, the sheriff said.

“It’s inexplicable,” Snyder said. “One of the first things we try to do at a crime scene is try to understand the motive of the offender … . In this case, we can’t establish a motive. It’s ‘I don’t know.”‘

Snyder said late Tuesday that Harrouff’s condition deteriorated and he may not survive. Earlier, Snyder said Harrouff suffered bruises, dog bites and cuts and had been jolted with a stun gun during his altercation with deputies.