Rudy Eugene, the man who was shot dead by police as he ate the face of a homeless man during Memorial Day weekend in Miami. (Photo by Miami Beach Police Department via Getty Images) (Photo by Miami Beach Police Department via Getty Images)

MIAMI (CBSMiami) – Rudy Eugene, the Causeway Cannibal who ate the face off a homeless man he attacked along the MacArthur Causeway, was apparently not high on bath salts or any other exotic street drug at the time of the attack, according to a report released Wednesday by the Miami-Dade Medical Examiner.

The news leaves law enforcement officials wondering what drove Eugene to strip off his clothes, attack homeless man Ronald Poppo, and chew off pieces of flesh from Poppo’s face.

Speculation about the cause of Eugene’s rampage on Poppo’s face centered on drugs, specifically bath salts, after police union officials claimed an increase in bizarre behavior among people on the street using such drugs.

PHOTO GALLERY: CAUSEWAY CANNIBAL ATTACK

The much-anticipated toxicology report released by Miami-Dade Medical Examiner Dr. Bruce Hyma found marijuana in Eugene’s system, something CBS4 News had previously reported, but no evidence of any other street drugs, alcohol or prescription drugs, or any adulterants found in street drugs.

The report said this includes cocaine, LSD, amphetamines (Ecstasy, Meth and others), phencyclidine (PCP or Angel Dust), heroin, oxycodone, Xanax, synthetic marijuana (Spice), and many other similar compounds.

Hyma’s office specifically ruled out bath salts, a class of synthetic drugs that have been known to cause bizarre behavior and overheating of people who use them, two things that made some believe Eugene’s cannibalistic behavior could be blamed on the 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 report said.

“Within the limits of current technology by both laboratories, marijuana is the only drug identified in the body of Mr. Rudy Eugene.”

The news from the medical examiner sends investigators back to square one as they look for what caused Eugene’s bizarre behavior.

PHOTO GALLERY: NOTORIOUS CANNIBALS IN HISTORY

A girlfriend and a friend who had seen Eugene hours before the attack said he had used marijuana, but had seen him use no other drug before traveling to the Urban Beach Weekend on Miami Beach the morning of the attack.

Eugene abandoned his car on the beach and walked back to Miami on the MacArthur Causeway, stripping off his clothes during the three-mile trip, and at one point he was spotted swinging from a lamp post.

Once on the Miami side of the causeway, he encountered Poppo where the MiamiMover crosses the causeway, in view of security cameras atop the Miami Herald building. Those cameras detailed how the naked cannibal attacked the much older Poppo, knocked him to the ground, and stripped him of his clothing.

Once overcome, Eugene chewed flesh from Poppo’s face, but a later autopsy report found he did not actually eat it.

A police officer was called to the scene by people who spotted the bizarre attack. He tried to intervene but was forced to shoot, killing Eugene and apparently striking the badly wounded Poppo.

Poppo, who was taken to Ryder Trauma Center, survived the attack but has no memory of it. His face was virtually destroyed but doctors say much of it can be repaired.

Eugene’s family and friends say they are clueless about why he attacked Poppo, claiming the former high school football player and car wash employee had never shown such violent tendencies. Many believed drugs were to blame, but with Wednesday’s report the search has begun for a new cause for one of South Florida’s most bizarre crimes.