Police mystified by teen's 'random' face-biting attack

Austin Harrouff (Supplied)
Austin Harrouff (Supplied)

Florida police are trying to figure why a teenage university student fatally stabbed a couple in their garage and bit into the dead man's face.

Officers believe Austin Harrouff, a 19-year-old Florida State University student, might have been on hallucinogenic drugs when he attacked Michelle Mishcon, 53, and John Stevens, 59.

Police mystified by teen's 'random' face-biting attack

Michelle Mishcon and John Stevens (Facebook)

Harrouff was having dinner with his family at a popular sports bar on Monday night (local time) in Tequesta, north of Palm Beach when he stormed off, apparently angered by the slow service, CBS reports.

Martin County Sheriff William Snyder said his parents were so worried about his odd behaviour they called police and members of his fraternity to try and find him.

He walked in the direction of his father's house, but instead turned onto the street before it where he came across the couple sitting on a couch in the garage.

Police were called to the house around 9:20pm, and a neighbour who tried to help the victims was seriously injured.

The first officer to arrive tried to Taser Harrouff, but it didn't stop him. She then tried to pull him off Mr Stevens' body but couldn't. It eventually took other officers and a dog to subdue him. Mr Snyder said they didn't want to shoot Harrouff for fear they'd hit Mr Stevens.

He said Harrouff was "abnormally strong", making him suspect drugs were involved. However, blood tests came back negative for methamphetamine, cocaine, heroin and other common illicit substances.

It will take longer to test for less common hallucinogens such as bath salts or flakka - a synthetic drug which was popular in south Florida briefly in 2014 and 2015, but fell out of favour after due to its serious side-effects.

Ms Mishcon was found dead in the garage, while Mr Stevens died in the driveway. Mr Snyder says they suffered serious injuries, including stab and slicing wounds. Mr Stevens also had "substantial trauma" to his face from bite marks.

Harrouff was taken to hospital and is in a critical condition. When he was admitted, Mr Snyder said he was making "animal-like" sounds.

Mr Snyder said there didn't appear to be any relationship between Harrouff and the couple, calling the attack "as random as random can be".

"Not one thing in this case seems to make sense," he said.

 "We can't get our footing in understanding motive or how this happened."