The FBI agent brother of an NYPD cop accused in a murder-for-hire plot killed himself while out of town with other agents, law-enforcement sources told The Post on Wednesday.

Salvatore “Sal” Cincinelli, 41, was found with at least one gunshot wound inside the Container Bar in Austin, Texas, when cops arrived there shortly before midnight on July 16 in response to a report of gunfire, a spokeswoman for the Austin Police Department said.

The incident is being investigated as suicide, the spokeswoman said. She wouldn’t elaborate.

Cincinelli was a former Wall Street trader who joined the FBI in 2011 and led financial-crime investigations in New York City before being promoted to the bureau’s headquarters in Washington, DC, according to biographical information posted online.

His younger sister, NYPD cop Valerie Cincinelli, 35, was busted by the FBI in May for allegedly scheming to have her estranged husband killed amid a bitter divorce. She’s being held without bail.

“She is absolutely devastated by the passing of her brother and best friend, and this is certainly adding to the stress of her current situation,” defense lawyer James Kousouros told The Post.

A since-deleted obituary said that Cincinelli died on July 17, and was buried in the Holy Rood Cemetery in Westbury, LI, on Monday following a funeral at St. Anthony’s Church in Oceanside.

In 2012, he was among several FBI agents interviewed by Reuters for a report on Wall Streeters who quit high-paying jobs to investigate financial crimes.

“Some of my friends said, ‘Are you crazy? Have you lost your mind?’” he said.

Cincinelli also said his wife was initially furious with his decision because she was worried about his safety and unhappy with the FBI’s lengthy training programs.

The FBI declined to comment on his death.