Mr. Decoste is being held at the Oakland County Jail in Pontiac, Mich., on charges unrelated to the killing in Nevada. The police in Henderson — who said in their affidavit for a warrant that Mr. Decoste had a criminal record that included episodes of home invasion, burglary and battery — are seeking to have him extradited.

According to the affidavit, which was filed in April, Mr. Decoste went to Mr. Capparelli’s home at least once after responding to the online advertisement. In an interview with a Henderson police detective, Mr. Decoste said it was for a “gig” taking photographs; in a separate interview, his girlfriend said it had to do with wrestling.

She also provided the police with a 9-millimeter Smith & Wesson handgun that had belonged to Mr. Decoste, the affidavit said. The caliber matched the cartridge casing found at the scene of the killing. Also among Mr. Decoste’s possessions was a watch that the police say had belonged to Mr. Capparelli.

The affidavit said several items were missing from Mr. Capparelli’s home, including his wallet, cellphone and house keys. It also said “investigators located a printed out Craigslist ad which had been placed by the victim. The ad sought out ‘young and good looking men’ who would be willing to wrestle and or compete in ‘submission matches.’”

Image John Capparelli Credit... Robert Sciarrino/NJ.com and The Star-Ledger

It was unclear whether this was the advertisement to which Mr. Decoste responded.

According to the affidavit, Mr. Decoste denied owning a gun and said he had had minimal contact with Mr. Capparelli and left his home shortly after meeting him.