(CNN) Joshua Brown teared up as he testified last month in the murder trial of a former Dallas police officer convicted of shooting and killing their neighbor in his own home.

Brown, a key witness in the trial, lived across the hall from Botham Jean at Dallas' South Side Flats apartments last year when officer Amber Guyger walked into Jean's apartment, mistaking it for her own, and killed Jean.

Brown was killed Friday at his current home, the Atera Apartments, about five miles from his former complex where he, Guyger and Jean all lived.

Before his own death, Brown lived in constant fear of gun violence, said Lee Merritt, an attorney for Brown's family.

Authorities have not said whether there's any connection between Brown's death and his testimony in Guyger's trial, which ended last week.

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