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, a former high school football defensive lineman and wrestler, 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 at a restaurant a short distance away 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 a futile attempt to find him before the attack.

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, because it is the motive of the offender that gets us going in the right direction. In this case, we can’t establish a motive. It’s ‘I don’t know.’”