A 19-year-old Florida State University student charged with fatally stabbing a couple and biting the dead man's face remains under surveillance with guards by his side at a hospital.

Martin County Sheriff William Synder said Austin Harrouff was incoherent and making "animal-like noises" when he was taken to a hospital after the Monday night attack.

Snyder said Tuesday that Harrouff's condition was "life-threatening." West Palm Beach television station WPTV (http://bit.ly/2b0lqH8 ) reports Harrouff was sedated and on a ventilator Wednesday.

Snyder says Harrouff tested negative for a number of drugs, including methamphetamine. Results for substances known to cause excited delirium — such a flakka and bath salts — are pending. Synder noted that Harrouff didn't have the raised body temperature often associated with flakka use.

Authorities say 53-year-old Michelle Misccon and 59-year-old John Stevens died and their neighbor was injured trying to fend off the attacker.