By Jim Forsyth

SAN ANTONIO (Reuters) - An assistant district attorney was shot and killed as he walked from his car to a Dallas-area county courthouse on Thursday, and his assailants were at large, police said.

"As the assistant district attorney was walking to his office, he was assaulted by an unknown assailant and he was shot multiple times," Kaufman Police Chief Chris Aulbaugh told reporters. Kaufman is a town of about 8,000 people southeast of Dallas, Texas.

The Kaufman County Sheriff's Office identified the victim as Mark Hasse, a former Dallas County prosecutor, according to the Dallas Morning News.

The shooting occurred on the same day the U.S. Department of Justice said in an unrelated statement that the Kaufman County District Attorney's Office was helping to investigate the Aryan Brotherhood of Texas, a gang that was established within the 1980s in the Texas prison system.

It was not immediately clear if the shooting was connected to the investigation.

Kaufman County Sheriff David Byrnes said authorities were searching for two people who fled in a Ford Taurus.

The courthouse and several structures including school buildings in the small community were briefly locked down, officials said.

(Additional reporting by Corrie MacLaggan; Editing by John Wallace and Cynthia Johnston)