By: WCTV Eyewitness News; CBS News

August 18, 2016

TEQUESTA, Fla. (WCTV) – Authorities are continuing to investigate what led to a gruesome double homicide in Tequesta, Florida on Monday night.

19-year-old Florida State student Austin Harrouff is accused in the violent stabbing attack that left a couple dead and another man injured.

The Martin County Sheriff's Office says that John Joseph Stevens III, 59, and Michelle Karen Mischon, 53, were killed by Harrouff outside of their home.

Authorities say Harrouff had attacked the victims with a knife and when police arrived on scene, Harrouff was on top of Stevens in the driveway, biting the victim's face. Police say it took multiple deputies, a taser, and a police K-9 to subdue the “abnormally strong” teen.

Autopsies revealed that Karen Mischon died of blunt force trauma injuries and Joseph Stevens died of multiple stab wounds and blunt force trauma.

Deputies say Harrouff had no known connections to the victims and and the attack appeared to be random and unprovoked.

The family of Jeff Fisher, the man who was injured in an attempt to thwart the attack, released the following statement to WPEC:

“The family would like to thank everyone for the concern shown Jeff. We would especially like to thank all the first responders who came to his aid that night. Jeff is doing as well as can be expected but he has a long healing process to go through. We are very proud of Jeff and the courage he has shown while attempting to help his friends and neighbors. We have no other comments and ask you to give us time to come together as a family and begin to heal."

Fisher, 47, was released from the hospital on Thursday.

The Martin County Sheriff’s Office says Harrouff's preliminary drug tests for marijuana, cocaine, heroin, opioids, and methamphetamine came back negative, but additional testing is being conducted.

Authorities suspect Harrouff may have been under the influence of hallucinogenic drugs, such as flakka or bath salts. Officials say tests for those drugs have been sent to FDLE and results could take 1-3 weeks.

MCSO says Harrouff remains hospitalized but has been upgraded to stable condition. He is conscious but unable to speak due to a breathing tube.

Harrouff has not been formally charged in the case. The Martin County Sheriff’s Office is working with the State Attorney’s Office to determine the charges.

By: WCTV Eyewitness News / AP / CBS News

August 16, 2016

TEQUESTA, Fla. (AP) -- Authorities in Florida say a man who may have been on a hallucinogenic drug fatally stabbed a married couple, biting off part of the man's face before wounding a would-be rescuer.

Martin County Sheriff William Snyder said Tuesday that deputies captured 19-year-old Florida State University student Austin Harrouff as he was biting the dead man's face in their driveway in Tequesta, an affluent coastal community north of Palm Beach, Monday night.

The Martin County Sheriff's Office says that John Joseph Stevens III, 59, and Michelle Karen Mischon, 53, were the victims killed by Harrouff.

Deputies say Harrouff had no known connections to the victims and and the attack was random and unprovoked.

Deputies found Harrouff on top of Stevens and it took several attempts, K-9s and a taser to pull him off, according to Sheriff Snyder. Snyder said they didn't shoot Harrouff out of concern of also striking the victim.

Snyder also said the neighbor who tried to help, 47-year-old Jeff Fisher, was stabbed and remains hospitalized but is expected to recover.

"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.

Snyder told reporters at a press conference on Tuesday afternoon that Harrouff is currently hospitalized in grave condition.

Sheriff Snyder said prior to the attack, Harrouff had joined his family for dinner at a nearby Duffy's, a popular sports bar and restaurant. Authorities say Harrouff stormed out of the restaurant, 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.

About 45 minutes later, he apparently targeted the couple at random, the sheriff said.

FSU has confirmed that Harrouff is currently enrolled at the school. He was expected to return for the fall semester as a sophomore, majoring in exercise science.

FSU Police Maj. Jim Russell says the department has reached out to the Martin County Sheriff's Office to offer any assistance if needed.

Russell says FSUPD has had no prior contact with Harrouff.

The Martin County Sheriff's Office press conference can be viewed below: