Two men, reportedly masked and dressed entirely in black, gunned down a Kaufman County, Texas, prosecutor this morning as he walked to a city courthouse. The Dallas Morning News reported that the victim had been “heavily involved” in the investigation of members of the Aryan Brotherhood.

The entire area was locked down and a search continued this afternoon for the two men who were described as having fled in a silver older model Ford Taurus. Meanwhile, KHOU-TV in Houston reported that the slain prosecutor was Assistant District Attorney Mark Hasse, a man who was said to be widely respected among jurists.

County Judge Bruce Wood said that courthouse security in Kaufman, a North Texas town of about 6,700 people about 30 miles southeast of Dallas, was always tight but not in the parking lot where Hasse was killed, WFAA-TV reported. Wood described the attack on Hasse as an “ambush,” the Dallas television station said.

The Aryan Brotherhood (AB) is a large, white supremacist prison gang that is infamous for its violence and its sprawling criminal empire, which also is highly active outside the nation’s prisons.