A businessman is putting up a $100,000 reward for information that helps authorities solve the murder of Joshua Brown — the Dallas man who was murdered after taking the stand in killer cop Amber Guyger’s trial.

Bill Perkins, an energy hedge fund manager and high-stakes poker player, is offering the reward, activist Shaun King announced on Twitter Sunday.

“My friend and brother Bill Perkins @bp22 is providing $100,000 for the reward to help us find who murdered Joshua Brown. Joshua was executed. He was a lead witness in the murder of Botham Jean,” King tweeted, erroneously adding that Brown — who previously lived across the hall from Jean — was killed in the same apartment complex, when he was actually shot in the parking lot of his new home, about 5 miles away.

Perkins retweeted King’s post and wrote, “Every murder is sad. The particulars around this specific set of circumstances make it important that everyone learn why this happened irrespective of the outcome. Either way a killer needs to be caught & I wish in every case these resources could be brought to bear for justice.”

Brown, 28, was gunned down Friday just 10 days after providing key testimony about the night of neighbor Botham Jean’s murder, according to police.

Lee Merritt, who represents the Jean family, said Brown repeatedly expressed concerns that testifying would put his life at risk.

Brown fled the state for California, where he remained as the trial got underway, according to Merritt.

But prosecutors “hounded him” and threatened to issue a warrant for his arrest if he didn’t appear in court. “So he got on a plane and came straight from the airport to the courthouse,” Merritt said.

No suspects or motives have been identified in Brown’s murder.

Guyger, 31, was convicted last week in Jean’s murder and sentenced to 10 years behind bars.