Officials performing an autopsy Monday noticed an indication of cyanide poisoning, leading police to cordon off streets as they investigated at the downtown hotel where the man's body was found.

The Burnsley Hotel was later declared safe, though the floor where the body was found remained off limits, said Fire Department spokesman Alex Paez. Streets reopened later Monday.

A hazardous materials team found white powder in a bottle in the man's fourth-floor room and was trying to determine what it was, Paez said.

It appears the man was dead for several days before his body was found, police spokesman John White said. Nothing suggests foul play.

The Democratic National Convention opens in Denver this month, but The Burnsley is not on the list of hotels where delegates are staying.

Five rooms on the fourth floor were occupied, and those guests were moved to other floors.

The Centers for Disease Control and Prevention describe cyanide as a fast-acting chemical that prevents the body from processing oxygen. It can be used in manufacturing, metallurgy and pest extermination.