A man who had been dead several days in a room at the Burnsley Hotel in Capitol Hill may have had traces of cyanide poison in his system, Denver police said Monday.
So far, detectives have not found any evidence to suggest that the man was a victim of foul play, police said.
A full autopsy is expected to be completed by today.
Special Agent Kathy Wright, spokeswoman for the FBI, said the bureau's hazardous materials team was assisting Denver police and firefighters in the investigation.
The only detail about the victim that authorities released Monday was that he was a black male. They were attempting to notify relatives before releasing his identity.
Police were called around 10 a.m. Monday about a dead body in one of the rooms of the Burnsley Hotel in the 1000 block of Grant Street.
The body was taken to the Denver coroner's office, where medical examiners determined the victim may have suffered cyanide poisoning, according to police.
After learning that cyanide may have been involved, police, firefighters and the FBI team returned to the hotel about 1:30 p.m. to continue their investigation. They found an unknown substance and were trying to determine what it was, police said.
The fire department's hazardous materials team tested for cyanide throughout the building and didn't find any additional evidence of the substance, Cmdr. Joe Hart said.
Tenants, who had been evacuated as a precaution, were allowed to return to their units, except for those on the fourth floor where the victim was found. They were barred from re-entering throughout the day.
"After we did the testing, we didn't think there was any threat to anybody else in the building," Hart said.
Cyanideis a potentially deadly poison that affects the body's ability to use oxygen, according to the Web site Medicine Health. Breathing cyanide gas causes the most harm, but experts say swallowing the substance can also be toxic.