Rudy Eugene—the Florida man who was suspected to be high on "bath salts" last month when he was shot and killed by police after refusing to stop chewing a homeless man's face—was not on "bath salts" after all.

According to the Miami-Dade County medical examiner's office, toxicology tests performed on Eugene found marijuana in his system, but no street drugs, prescription drugs or alcohol. Eugene also tested negative for adulterants commonly mixed with street drugs.

"The department has also sought the assistance of an outside forensic toxicology reference laboratory, which has confirmed the absence of 'bath salts,' synthetic marijuana and LSD," the medical examiner said.

But that doesn't necessarily mean cannabis was the cause of cannibalism.

"There is an almost infinite number of chemical substances out there that can trigger unusual behavior," Bruce Goldberger, professor and director of toxicology at the University of Florida, told the Associated Press. "There are many of these synthetic drugs that we currently don't have the methodology to test on, and that is not the fault of the toxicology lab. The challenge today for the toxicology lab is to stay on top of these new chemicals and develop methodologies for them, but it's very difficult and very expensive. There is no one test or combination of tests that can detect every possible substance out there."

Ronald Poppo, the 65-year-old homeless victim, remains hospitalized following the May 26 attack.

[Related: How do 'bath salts' drive people crazy?]

According to the American Association of Poison Control Centers, the use of "bath salts" appears to be on the rise, with poison control centers fielding 20 times as many calls related to the "drug" in 2011 as they did in 2010. And "bath salts" have been linked to a string of bizarre crimes in the United States in recent months.

On June 3, police in Illinois said a 37-year-old man admitted to using "bath salts" before a robbery attempt in which he "dismantled a fan, plugged in a hair dryer, pulled out wires from a furnace, toyed with a hatchet and managed to pour gasoline on himself." Officers used a stun gun to subdue him.

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[Also read: Use of 'bath salts' on the rise]

But other drugs have been linked to bizarre behavior, too. On Wednesday, a Texas judge revoked bond for a 22-year-old man who allegedly killed and began eating his roommate's dog "after chasing a neighbor on his hands and knees while growling." Police say the man had taken K-2, a form of synthetic marijuana, before the the attack.