FORT LAUDERDALE, Fla. » A 19-year-old Florida State University accused of killing a random Martin County couple and then biting the man’s face remained in stable but critical condition today as investigators try to piece together what sparked the attack.

Austin Harrouff, who was visiting South Florida while on break, is facing charges of first-degree murder in the deaths of John Stevens III, 59, and Michelle Mishcon, 53.

Harrouff, who had no criminal history, left Duffy’s Sports Grill during a family dinner Aug. 15, walked about three miles and then attacked the couple, Martin County Sheriff William Snyder said. A neighbor, 47-year-old Jeff Fisher, was stabbed several times when he tried to intervene. He has been released from the hospital.

Investigators are waiting for Harrouff to become more alert for questioning and for the FBI to provide the results of a drug test. Harrouff is expected to be released from St. Mary’s Medical Center in West Palm Beach early this week, according to the Martin County Sheriff’s Office.

Harrouff tested negative for common street drugs, such as methamphetamine, cocaine, heroin and marijuana. The FBI is conducting a more extensive test that would detect the presence of bath salts and flakka.

A stun gun seemed to have no effect on Harrouff, who appeared to have “abnormal strength,” Snyder said. It took several deputies and a canine to subdue Harrouff.

Harrouff told deputies after the attack, “Test me, you won’t find any drugs,” officials said.

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©2016 Sun Sentinel (Fort Lauderdale, Fla.)