(CNN) -- A prosecutor was gunned down outside a Texas courthouse Thursday morning, a law enforcement source with knowledge of the shooting said.
Mark Hasse is an assistant district attorney for Kaufman County and had earlier worked for the district attorney's office in adjacent Dallas County, the source told CNN.
Hasse was killed in the shooting, CNN affiliate WFAA reported.
Authorities were searching for a suspect or suspects, said Kaufman County Sheriff Public Information Officer Pat Laney.
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.
The Kaufman County courthouse was in lockdown, said Mary Ann Gronewald, chief deputy of the Kauffman county clerk's office.