(CNN) — A Texas district attorney vowed Thursday to catch the "scum" who gunned down one of his assistant prosecutors outside his office near Dallas on Thursday morning.
Mark Hasse, an assistant district attorney in Kaufman County, was shot to death while getting out of his car Thursday morning, sheriff's spokeswoman Pat Laney told CNN. His boss, District Attorney Mike McLelland, called him "a stellar prosecutor" who knew threats were part of the job.
"I hope that the people that did this are watching, because we're very confident that we're going to find you," McLelland said at a news conference Thursday afternoon. "We're going to pull you out of whatever hole you're in, we're going to bring you back and let the people of Kaufman County prosecute you to the fullest extent of the law."
Police have interviewed several witnesses to the killing and are pursing "many leads," Kaufman Police Chief Chris Aulbaugh said. But they had made no arrests, and they appealed to the public for help.
Investigators are looking for an older-model, four-door sedan, either brown or silver, but it wasn't clear whether there were one or two suspects Thursday afternoon, Laney said.
"We have officers going over all of this case," she said. "Nothing has been identified yet that could have prompted this assault."
The FBI joined the search Thursday afternoon, offering assistance to the Kaufman County authorities, said Katie Chaumont, a spokeswoman for the bureau's Dallas office.
Hasse "was a very well-liked person" who had worked for the district attorney's office in Dallas County, Laney said.
The courthouse in Kaufman, about 30 miles east of Dallas, was locked down after the shooting. An e-mail circulated in the Kaufman County district attorney's office is advising prosecutors to be vigilant and careful in their own personal security, said a spokesperson for the office.
CNN's Marlena Baldacci, Nick Valencia and John Branch contributed to this report.
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