The incredibly twisted tale of the college student suspected of killing a Florida couple on 15 August, and biting the face of one of the victims, has become even more bizarre. Officials have now also revealed that the dead man was also bitten in the abdomen, and that human tissue had been recovered from the the suspect's mouth.

Teenager Austin Harrouff also allegedly dared police to check him for substances when he was arrested for the murders, saying: "Test me. You won't find any drugs," said Martin County Sheriff's Office spokeswoman Trisha Kukuva.

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Officials are still stunned by the crimes and scrambling to find some explanation. "This is so difficult for all of us to process," Martin County Sheriff William Snyder told the Miami Herald. "To all of us, none of this makes sense. There's just not one thing in this case that seems to make sense."

"I have never seen a scene that had this much savagery and this much violence, ever," the sheriff told the local CBS station. "He was biting the victim in the face area and the abdomen area, and we did recover some remnants of human tissue from his mouth."

Harrouff, 19, had never before been in trouble with the law when he suddenly stormed out of a sports bar during dinner with his family, reportedly in a rage over poor service.

As he walked for miles in Tequesta, Florida, he happened upon married couple John Stevens, 59, and Michelle Mishcon Stevens, 53, relaxing in their remodeled garage with the door open. Even though they were complete strangers to Harrouff, he allegedly attacked and killed them. A neighbour came to their aid with a knife in his pocket and other tools in the garage, said police.

It took stun-gun jolts, a police dog and several officers to pull the "abnormally strong" Harrouff off Stevens as he chewed on the man's face and "grunted" like an "animal", according to police.

Authorities have released surveillance video of Harrouff walking out of Duffy's, a Jupiter sports bar, shortly before the attack. He's wearing white shorts, a blue shirt and baseball cap bearing the phrase Make America Great Again, the campaign slogan for GOP presidential candidate Donald Trump.

Harrouff, who is under armed guard, is in stable but still serious condition in a Palm Beach County hospital. Police haven't yet been able to question him. He is sedated and on a breathing tube. It's as yet unclear why his health is so precarious.

Though he was a standout high-school athlete and good student at Florida State University, his mother told police he had suddenly been acting strangely for two weeks before the attack, believing he had super powers and that he was on the Earth to protect people.

In a series of YouTube videos, he talked of a decision to stop using steroids for body building, and referenced his "psycho side".

Harrouff has tested negative for drugs such as cocaine, marijuana and heroin. But authorities are still awaiting the results of FBI tests for other dangerous substances such synthetic drugs flakka and bath salts, which can cause bizarre violent outbursts.

Harrouff will be charged with two counts of first-degree murder and one count of first-degree attempted murder for the attack on the neighbour, said authorities.

The children of the victims are calling for his execution. "It is not super important to me what his mindset was," John Stevens IV told the Sun Sentinel​. "I just want to see the prosecutor ask for the death penalty. I want him to go through that process and to pay for what he did."

NOTE:
- This article was altered to reflect Harrouff's status.