A 19-year-old Florida State University student with no criminal record was found biting a dead man's face in South Florida on Monday at the scene of a deadly stabbing, authorities said.

Martin County Sheriff William Snyder told reporters that Austin Harrouff may have been on hallucinogenic drugs when he attacked Michelle Mishcon, 53, and John Stevens III, 59, at their Tequesta, Florida, home.

Police pronounced Stevens dead at the scene, and later found Mishcon's body inside the couple's garage. She is the daughter of the former mayor of North Miami Beach.

Martin County Sheriff’s Office officials said a female deputy arrived and found Harrouff on top of Stevens attempting to eat his face.

"When she got there she realized that the offender was actually biting the victim in the face and causing what turned out to be some substantial trauma to his face from bite marks," Sheriff William Snyder said.

Deputies were initially unsuccessful in getting Harrouff off of the victim with a stun gun and K-9 dog, officials said. Eventually, four deputies were able to pry him off and arrest him.

A neighbor who initially came to the home to try and help was also stabbed by the suspect and taken to a nearby hospital for surgery. The neighbor, 47-year-old Jeff Fisher, is expected to survive.

"He's recovering. He's got multiple stable wounds in the left side of his head and in his back," his father Steve Fisher said.

"I think he had a knife," Jeff Fisher told a 911 operator in a tape of the call released Tuesday. Breathing heavily and bleeding profusely, Fisher told the dispatcher the assailant had attacked a woman, who was lying motionless on the driveway, and then him when he tried to intervene. When asked if he knew the man, he replied, "I have no idea."

Harrouff was also taken to a hospital for treatment after the incident. Officials said he was in life-threatening condition and it's unknown if he'll survive.

Snyder told reporters that a motive is not yet known, but has not ruled out the influence of a drug such as flakka. Authorities are running tests for multiple substances, Snyder said.

"We will be doing sampling of his blood to see if there was flakka or bath salts, which are known to cause what we call the excited delirium, and he did have some indications that we might be working with that," Snyder said.

Snyder added the couple did not know Harrouff and that the Florida State University student gave a false name when first arrested, slowing the investigation.

Harrouff's attorney said he was working at home for the summer and taking college courses. She said he has no criminal history but couldn't comment if drug use spurred the attack.

"There are mental health issues that will have to be investigated here, we don't know if anything is going to show up on toxicology reports, there's a lot of unknowns and unanswered questions and things we may never know," attorney Michelle Suskauer 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.'"

A sophomore majoring in exercise science, Harrouff is muscular -- he wrestled and played football at Suncoast Community High School in nearby Riviera Beach. Football teammates said 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.

Stevens owned a lawn service and the couple enjoyed boating, neighbors said.

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

"It was the cutest thing," Lourie said.

She said it isn't surprising Fisher would try to rescue them, saying he and the couple were close friends.

Doctor Wade Harrouff, a dentist, declined to comment about his son's arrest.