A veteran San Antonio police detective was shot and killed around 11:45 a.m. on Sunday.

SAPD Detective Benjamin Marconi, 50, was gunned down during a traffic stop that happened right outside San Antonio Police headquarters.

During a press conference, San Antonio Police Chief William McManus said Detective Marconi pulled over a driver for an unknown traffic violation. While Detective Marconi was writing the first driver a ticket, another driver pulled up behind Detective Marconi's vehicle, walked up to the driver's side door and shot him twice in the head. The suspect then drove away in the vehicle pictured below. The car appears to be a black sedan -- possibly a Toyota or Nissan -- with chrome rims and dark windows.

Witnesses who called police described the suspect as a man in his 20s or 30s with a "dark complexion." Chief McManus said the suspect is between 5-foot-7 and six feet tall and was wearing a gray sweatshirt and black baggy pants at the time of the shooting. The suspect also may have a beard, but there are conflicting reports about his facial hair. As of late Sunday afternoon, the suspect was still at large and police said he was considered armed and dangerous.

Detective Marconi, a 20-year veteran of law enforcement, was pronounced dead at a San Antonio area hospital around 12:30 p.m.

Police said they still do not have a motive for the shooting. But, officers are actively pursuing all leads. Chief McManus said he does not believe the initial driver had any connection to the suspect.

Texas Governor Greg Abbott called the fatal shooting an act of horrific violence. He asked Texans to pray for the officer's loved ones.

"Attacks against law enforcement officers will not be tolerated in Texas and must be met with swift justice," Abbott said in a statement.

San Antonio Mayor Ivy Taylor also released a statement:

"I want to extend my deepest condolences to the family of the officer killed outside police headquarters today as well as to our entire police force. This type of crime cannot and will not be tolerated. I ask for the community's thoughtfulness and patience as the investigation continues and SAPD searches for the suspect."

Police are asking the public to call Crime Stoppers at 244-STOP if you have any additional information on the suspect.

This is a developing story. Check back for updates.