DENVER -- The FBI is now investigating a possible case of cyanide poisoning at a downtown Denver hotel.

Denver police were first on the case after they were called to The Burnsley Hotel at about 10 a.m. Monday on the report of an unresponsive party. Officers found a black man, in his 30s or 40s, dead inside Room 408.

The man appeared to have been there several days, police detective John White said.

Officers called the coroner to the hotel to pick up the man's body. Hours later, the medical examiner's office called police to say that during an initial examination, it appears that the man's body had a substance "consistent with cyanide." It's not clear if the man inhaled it, ingested it or touched it.

Denver firefighters and hazardous materials crews were called to the hotel, which is about four blocks from the Colorado State Capitol, to investigate. Investigators found a white substance in the man's room.

"The substance that was located on the fourth floor was a white powder substance. The amount was not specified," said Alex Daez, with Denver Fire.

Denver police won't say what the white substance is, but confirmed that the FBI has now taken over the investigation. Denver police officers found no evidence or information that suggests foul play.

The four people who had initially touched the man were decontaminated as a precaution. Five occupied rooms on the fourth floor were evacuated and patrons moved to another floor.

Eleventh to Ninth avenues from Logan to Sherman streets were blocked off for four hours but no evacuations were ordered. Roads reopened by 4:30 p.m.

Cyanide can be found in a colorless gas or crystals.

There were reports of a strong odor of cyanide at The Burnsley hotel after the body was found. According to the Centers for Disease Control and Prevention, cyanide has a "bitter almond" smell, but not everyone can detect the odor and it does not always give off an odor.

One could be exposed to cyanide by breathing air, drinking water, eating food or touching soil that contains cyanide. Inhaling large doses of cyanide could cause comas, seizures, heart attacks, and even death after a few moments.

The exact cause of the man's death is not known until the autopsy is complete.

The Burnsley Hotel is located at 10th Avenue and Grant Street.

Additional Information:

Centers for Disease Control and Prevention's facts about cyanide.
The Burnsley Hotel