TownePlace Suites maintenance worker Mike Kellow told the operator Monday morning that he found the 38-year-old Gray's body in a corner of his room slumped against a wall.
"There's a hypodermic needle next to the bed here," Kellow said.
The dispatcher asked if Gray was awake.
"Oh God, no. He's all purple," Kellow said.
Kellow told the operator it appeared that Gray had been "gone a while."
Kellow says he checked on Gray after the bassist's mother called the Urbandale, Iowa, hotel because she couldn't reach her son.
The six-minute recording, which was first obtained by Des Moines television station WOI-TV on Wednesday, ends with the dispatcher telling Kellow he was sending a police officer to the hotel.
Keller did not immediately respond to a phone message Thursday seeking comment.
Urbandale police Sgt. Dave Disney said Thursday that everything in the hotel room was collected and documented, but he declined to elaborate on what investigators found.
"What was said on the tape is consistence with some things we found in the room, but that's all I'm going to say," Disney said.
Police have said there was no evidence of foul play or trauma, and an autopsy was inconclusive about how Gray died. Police are awaiting the results of toxicology tests, which could take up to six weeks.
In 2003, Gray acknowledged that he was on drugs when his red Porsche collided with another car that year in Des Moines. No one was seriously injured. Under a plea agreement, prosecutors dropped charges of possession of marijuana, cocaine and syringes.
Media reports at the time noted that court records included a handwritten note from Dr. Joe Takamine that described discussions with Gray that were "very frank and open about his sporadic use of various drugs and of the long periods of abstinence in between."
Gray was one of the founding members of the Des Moines-based band known for its grotesque masks, thrashing sounds and aggressive, dark lyrics.
Gray's wife, Brenna Gray, is pregnant. She and surviving members of the band held a news conference on Tuesday.
She said their unborn daughter will grow up knowing her father for the legacy he left behind.
Slipknot emerged in the mid-1990s, and its 1999 debut album sold about 2 million copies. The band won a Grammy in 2006 for best metal performance for the song "Before I Forget."
Slipknot's last studio album, "All Hope Is Gone," debuted at No. 1 on the Billboard charts in 2008, and concert industry trade publication Pollstar ranked Slipknot 18th in its Top 20 Concert Tours list in 2009.
The band has been on a yearlong hiatus.
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