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Almost a year before he testified as a key witness in the Amber Guyger murder trial, Joshua Brown was wounded in a shooting at a Dallas strip club that left another man dead, police said.

Brown believed he was the target in that November 23 strip club shooting and felt there were “still people out there who wanted to do him harm,” said attorney S. Lee Merritt, who represents Brown’s family.

Last Friday, Brown was shot to death in the parking lot of his Dallas apartment complex. No arrests have been made. The killing happened 10 days after Brown testified for the prosecution against Guyger, the former Dallas police officer who was convicted of killing her neighbor, Botham Jean.

Now, a mystery now surrounds the death of Brown, a relatively unknown 28-year-old who reluctantly testified in the murder case.

Several presidential hopefuls have urged authorities to solve the case. Merritt has called for an independent investigation into the killing, acknowledging that speculation has begun to spread. He said it “doesn’t mean there’s evidence” of police involvement or connection to the Guyger case.

“This case must be resolved, and that investigation that leads to finding the person must be seen as trustworthy or transparent by the community,” Merritt said Monday on “Anderson Cooper Full Circle.”

Dallas police said they are investigating Brown’s death. Police declined to comment to CNN on the call for an independent investigation.

The NAACP Legal Defense and Educational Fund, Inc. (LDF) also requested an investigation into Brown’s death.

“We urge state or federal authorities to follow the trail of misconduct left by this case and fully investigate the circumstances surrounding Mr. Brown’s death,” LDF’s President and Director-Counsel Sherrilyn Ifill said in a news release.

“It is critical to public confidence in the administration of justice that witnesses who speak out against police violence are fully protected. The suspicious circumstances of Mr. Brown’s killing should cause great alarm and demand an immediate and piercing inquiry.”

Mayor Eric Johnson said in a tweet Dallas police would “conduct a thorough investigation.” “Until we know more about this incident, I encourage everyone to refrain from speculation,” Johnson posted.

Witnesses told police they saw a silver, four-door sedan speeding out of the parking lot right after the shooting in the Atera Apartments parking lot.

The strip club shooting

Jean was shot and killed by Guyger on September 6, 2018. On November 23, Brown was shot at a strip club, Dallas Cabaret South, according to a police blotter item. A full police report on that shooting was not immediately available.

Citing an affidavit, the Dallas Morning News reported that a man had waited for Brown outside the club and the two fought. The man started shooting when Brown tried to leave, wounding his foot, the newspaper reported. Nicholas Shaq’uan Diggs, 26, was killed.

Kendall Morris, 26, was indicted in June for murder and aggravated assault with a deadly weapon, court records show. He pleaded not guilty and is out on bond, his attorney, Henry Campbell, told CNN on Monday.

Campbell said Morris had “nothing to do with what happened to Josh.” Morris had “no reason to want to retaliate” because he is innocent of the November shooting, Campbell said.

He said investigators have not spoken with Morris since Brown was killed.

Seeking ‘a low profile’

Brown tried to keep “a low profile intentionally until some of the heat” from the strip club shooting died down, Merritt said. Brown moved out of the South Side Flats apartment complex where he, Guyger and Jean had all lived.

Merritt said Brown was subpoenaed to testify in Guyger’s trial, but “made it clear he had no interest in testifying in open court in that trial.”

“I think he had some apprehension about being seen as an informant or a snitch,” Merritt said.

He said Brown had “personal beef” with people who did not know he was still in the city.

Testimony at Guyger’s trial

Jean, a 26-year-old accountant, was killed when Guyger said she mistakenly walked into his apartment, one floor above her unit, and mistook him for a burglar.

Brown said he returned home that night from watching a football game at a sports bar around the same time Guyger walked into Jean’s apartment. Brown was down the hall when he heard voices of two people who sounded like they were meeting by “surprise,” he testified.

He heard shooting “right after.” He testified he didn’t hear any police commands like “Show me your hands,” before hearing the gunshots. But he said it was difficult to make out the words between Guyger and Jean.

Soon after, Brown said, he saw Guyger enter the hallway from Jean’s apartment, talking on the phone.

Joshua Brown was overcome with emotion on the witness stand during the Amber Guyger murder trial.

She was “crying, explaining what happened, what she thought happened, saying she came into the wrong apartment,” Brown testified.

Through his peep hole, Brown said he also saw the former officer “going back, back and forth on the phone.”

“And then, I think she went back inside, then came back out,” Brown said.

He broke down during the testimony and wiped away tears with his T-shirt.

Guyger was convicted of murder and sentenced to 10 years in prison last week.

A family mourns

Merritt said Brown’s mother knew her son was “really bothered by the fact that he was given a lot of exposure from the trial, a lot of unwanted attention.”

Brown said during the trial that he studied interdisciplinary science at the University of South Florida, where he played football. In a statement, the school said he “was a much loved and valued member of our football program and athletic family.”

“His loss is felt by many whose lives he positively touched,” the school said.

On Monday, Brown’s family prepared to bury him.

“They’re devastated,” Merritt said. “They were at the funeral home viewing Joshua Brown’s body for the first time and making funeral arrangements.”

CNN’s Ashley Killough, Holly Yan and Sheena Jones contributed to this report.