A 19-year-old Florida State University student accused of killing two people and trying to bite the face off one victim had no criminal record before the shocking incident, investigators said Tuesday.

Michelle Mishcon, 53, and John Stevens, 59, were stabbed to death at their Tequesta home, where investigators found Stevens' body in the driveway and Mischcon's corpse in the garage. Both suffered an "unusual amount of trauma," Martin County Sheriff William Snyder said. But it’s when investigators saw the alleged attacker, Austin Harrouff, that the gory details of the crime became apparent, The Palm Beach Post reported.

“He was biting the victim on the face and actually removing pieces of his face with his teeth,” Snyder told reporters, including those from The Orlando Sentinel.

Harrouff had been eating dinner with his family at a restaurant a short distance away when he stormed off, apparently agitated about slow service, Snyder said Tuesday. Harrouff's 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.'"

Snyder said Harrouff stormed out of the restaurant at about 8:30 p.m. He said the would-be rescuer called 911 at 9:20 p.m. to report the attack, which apparently began in the garage where the couple liked to sit at night.

Harrouff is muscular -- he wrestled and played football at Suncoast Community High School in nearby Riviera Beach.

A neighbor who stumbled upon Harrouff and tried to intervene was also stabbed and had to be flown to Palm Beach County Hospital, authorities said. That person sustained “substantial trauma," but is expected to survive.

A stun gun had little effect on Harrouff, officials said, and it took a K-9 and several officers to subdue and restrain him.

Harrouff initially gave investigators a false name. He is currently enrolled at Florida State University and was "apparently getting good grades."

"The suspect in this case was abnormally strong," Snyder said, making him think Harrouff was on drugs. He said hospital blood tests showed no signs of methamphetamine, cocaine, heroin or other common drugs; it will take longer to test for less common hallucinogenic drugs such as flakka or bath salts.

“It absolutely could be a flakka case. We don’t know,” Snyder told WPTV. “It will be some time before we get any kind of toxicology report. I would not be surprised though if we end up finding that is the case.”

Harrouff was also taken to a hospital for undisclosed treatment.

The Associated Press contributed to this report.