A 19-year-old frat boy who was found at the scene of a double homicide on Monday biting flesh off a victim's face could have been on the synthetic drug flakka, authorities believe.

Austin Kelly Harrouff, whose condition is deteriorating in the hospital, was arrested Monday night after allegedly stabbing married couple Michelle Stevens and John Stevens III to death inside their Jupiter, Florida, home.

Sheriff William Snyder said a toxicology report would not be immediately available, but added: 'It absolutely could be a flakka case. We don’t know...I would not be surprised though if we end up finding that is the case.'

The synthetic drug swept Florida in 2013, gaining the nickname 'five dollar insanity' because it causes hallucinations, psychosis and 'superhuman' strength.

In a released 911 call, the couple’s neighbor, Jeff Fisher, 47, can be heard breathing heavily after he heard screams and rushed to the Stevenses' house on Southeast Kokomo Lane to help, only to be stabbed several times himself.

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Cannibal attack: FSU student Austin Harrouff, 19 (left), is accused of stabbing to death Michelle and John Stevens (pictured together right), and biting pieces off the husband's face in Jupiter, Florida

Grisly scene: Deputies were summoned to the Stevenses' home on Kokomo Lane to discover Harrouff on top of John Stevens III, biting him and growling, according to police

Michelle, 53, was found dead from stab wounds inside the couple's garage (pictured)

When law enforcement arrived on the scene, they found the Florida State University student on top of John, tearing pieces of his face off with his teeth in the driveway.

Deputies later discovered Michelle's lifeless body inside the garage of their home.

A female deputy used a stun gun on Harrouff several times in an attempt to subdue him, but it failed to work.

It took four deputies and a K9 to pry Harrouff off the victim; the suspect was described by Martin County Sheriff William Snyder as ‘grunting and growling,’ and ‘making animal noises’ at the time of his arrest.

Snyder said the responding deputies didn't shoot at Harrouff, fearing their bullets would strike the victim, as they did not know that John was already dead.

Harrouff was out to dinner with his parents at the sports bar Duffy's West (pictured) when he became agitated and left during the meal, prompting his parents to call the police over his bizarre behavior

Harrouff walked four miles north towards his father's house, but inexplicably turned onto the 19000 block of Southeast Kokomo Lane where the Stevenses were sitting in their garage

This 2015 file photo shows confiscated vials of flakka, the emerging drug that can alter brain chemistry in such a way that users can't control their thoughts

What is flakka? Flakka, also known as gravel, has become a growing problem for police after bursting on the scene in 2013, partly because it costs just five dollars or less for a vial. It is the latest in a series of synthetic drugs that include Ecstasy and bath salts, but officials say flakka is even easier to obtain in small quantities through the mail. Flakka's active ingredient is a chemical compound called alpha-PVP, which is on the U.S. Drug Enforcement Administration's list of the controlled substances most likely to be abused. It is usually made overseas in countries such as China and Pakistan. Jim Hall, an epidemiologist at the Center for Applied Research on Substance Use and Health Disparities at Nova Southeastern University, said: 'The individual becomes psychotic, they often rip off their clothes and run out into the street violently and have an adrenaline-like strength and police are called and it takes four or five officers to restrain them. Advertisement

'The suspect in this case was abnormally strong,' Snyder said. 'So getting that excited delirium type increased adrenaline strength.

'Somebody not feeling pain, not responding to a dog bite, repeated stuns from a Taser, taking three to four deputies and officer dog to get him off. That’s somebody with a lot more strength than you would normally encounter.'

While initial drug tests came up negative for cocaine, methamphetamines, marijuana and opiates, investigators will also be testing Harrouff for flakka and bath salts.

Snyder said: 'I’m not going to speculate, except to say that we know in our business that people on flakka or bath salts will do this type of behavior, where they attack the victim and do the biting and actually remove pieces of flesh in the bites.'

Despite some signs that Harrouff may have been under the influence of flakka, he did not have a raised body temperature, common among users of the drug, the Palm Beach Post reported.

Flakka, which contains alpha-PVP, a chemical compound similar to ingredients used to make bath salts, resembles a mix of crack cocaine and meth.

Once ingested, the drug causes a feeling of euphoria, hallucinations and sometimes psychosis or apparent superhuman strength.

Jim Hall, an epidemiologist at the Center for Applied Research on Substance Use and Health Disparities at Nova Southeastern University, said: 'The individual becomes psychotic, they often rip off their clothes and run out into the street violently and have an adrenaline-like strength and police are called and it takes four or five officers to restrain them.

'Then once they are restrained, if they don't receive immediate medical attention they can die.'

On Tuesday evening, Snyder said Harrouff was sedated and intubated in the hospital after suffering cuts, bruises and dog bites.

He is currently in poor condition, with authorities believing he may have ingested something causing 'intestinal problems', the Treasure Coast Palm reported.

College kid: Harrouff, pictured left and right with his mom and dad, is a student at Florida State University

Harrouff, pictured right, with his dad, Wade (center), in Times Square, New York City

Frat boy: Harrouff traveled to Jupiter, Florida, with some of his fraternity brothers, members of Alpha Delta Phi (pictured)

Courtesy Local 10/WPLG

The son of a dentist, Harrouff wrestled and played football at Suncoast Community High School in Riviera Beach, where rosters listed him at 6ft tall and 200lbs.

Football teammates said he was a harmless teenager whose coaches wanted him to be more aggressive.

'The coaches would always try to get him mad and play angry, and he never had it in him. I didn't think he would hurt a fly,' quarterback Matt Dame told The Palm Beach Post. Dame now plays at Columbia University.

Joey Bashwiner, 19, said he attends FSU and also went to middle school with Harrouff.

'He seemed like a pretty normal kid,' Bashwiner told TCPalm. 'Nothing wrong, just quiet.'

During a press conference Tuesday, Sheriff Snyder said that Harrouff initially gave them a false name, Austin Michael Moore.

The sheriff said that a preliminary investigation has determined that Harrouff did not know the victims, and that the stabbings, which he described as 'inexplicable' and 'perplexing,' were random acts of violence.

According to Snyder, an experienced investigator said the stab wounds, massive lacerations and blunt force trauma made it as bad a case as he's ever seen.

Autopsy results show John died of stab wounds and blunt force trauma.

The autopsy on his wife, Michelle has not been completed.

'Harmless': A former teammate recalled that football coaches wanted Harrouff to be more aggressive, but he 'never had it in him'

Evening gone wrong: Harrouff, seen left and right, was having dinner with his parents at a sports bar when he became agitated and took off

The 19-year-old (pictured far right) is a rising sophomore at FSU studying exercise science

Star athlete: Harrouff wrestled and played football at Suncoast Community High School in Riviera Beach, Florida

Harrouff, a rising sophomore at FSU studying exercise science, lives a few miles away with his mother and was in town with some of his fraternity brothers, members of Alpha Delta Phi.

Snyder said at 8.30pm, Harrouff was out to dinner with his parents at the sports bar Duffy's West.

Harrouff appeared to walk towards his father Wade's (pictured) home, before he turned onto Kokomo Lane

According to his parents, Harrouff became agitated - possibly over slow service - and left during the meal.

They were so concerned they called the police, while his frat brothers went looking for him.

One Duffy's employee said the surveillance video had been handed over to authorities.

Harrouff is believed to have walked four miles away towards his father's house, but inexplicably turned left onto Southeast Kokomo Lane.

The Steveneses were sitting in the garage of their stucco home on Kokomo Lane with the door open, when the attack occurred at around 9.15pm.

Snyder, who said there was no link between Harrouff and the married couple, described the attack as 'random as random can be'.

Harrouff allegedly stabbed the couple with a switchblade knife he was known to carry around.

Multiple ‘weapons of opportunity,’ were also used to inflict massive trauma to the victims' bodies.

Michelle, 53, and John, 59, were pronounced dead at the scene

John (left) sustained severe damage and bite marks to his face after being stabbed to death in the driveway. Wife Michelle (right) was found dead in the garage

Michelle is pictured with her 26-year-old daughter, Ivy Stevens

John is seen here with his son, also named John Stevens

Snyder said it was clear that John had fought back.

‘There was an enormous amount of violence inside that garage,’ Snyder said.

In a 911 call released by the Martin County Sheriff’s Office, Fisher, who rushed over to help his neighbors, can be heard gasping for air before asking for police and medical help.

He said: 'I think he had a knife but I'm not positive.

'There's a girl laying on the ground, he beat her up.

'I ran over there, I'm bleeding profusely here at the moment, I don't know what happened. I've been stabbed in the back,' he told the dispatcher.

According to his father, Fisher was stabbed once in the neck, three times in the back and once in his side, CBS reported.

John owned a lawn service and the couple enjoyed boating, neighbors said. According to his wife's Facebook page, the two had been married for 19 years.

Michelle worked in finance and was the daughter of a former North Miami Beach mayor.

'John and Michelle were the nicest people,' neighbor Amy Lourie said. She said they would sit in the garage with the door open while watching television and wave and talk to passersby while their Labrador retriever played in the yard.

Investigators say Mr Stevens, pictured above with his wife on a fishing trip, fought back and suffered lacerations and blunt force trauma

Surprise attack: The married couple were attacked while sitting in their garage on a hot summer evening with the door ajar

She added that they would drive around the neighborhood in their golf cart with the dog sitting with them.

'It was the cutest thing,' Lourie said.

She wasn't surprised their neighbor Jeff Fisher would try to rescue them, saying he and the couple were close friends.

Fisher was taken to a hospital with five stab wounds, according to his father. He is expected to survive.

Austin Harrouff was also taken to the hospital, where he remained sedated Tuesday.