One police officer was killed and a second critically injured by a gunman in Louisiana on Sunday, in a shooting that started a four-hour standoff between the suspect, SWAT teams and police, officials said.

The officers, members of the Baton Rouge Police Department, were investigating a killing that occurred early Sunday when they were fired on by the gunman. The injured officer remained in critical condition at a hospital late into the night, Sgt. Don A. Coppola Jr. of the Baton Rouge Police said Monday.

The two officers, a 21-year veteran of the police department and a seven-year veteran, were shot after police responded to a tip that a suspect was on Conrad Drive in Baton Rouge, police said during a news conference. The names of the officers have not yet been released.

Chief Murphy Paul of the Baton Rouge Police Department said that the shooting and standoff began at about 9:30 a.m. Sunday as police searched for a suspect in a murder case.

Police received a tip about the suspect’s possible location in East Baton Rouge, Paul said, and “while our officers were checking scene” the gunman fired on them.

Two officers were struck by gunfire and taken to the hospital, and during the four-hour standoff that ensued the gunman and police traded shots at one another, Paul said. Eventually, after negotiations with SWAT teams, he surrendered and was taken into custody “without incident,” the chief said.

After news broke of the first officer’s death, Sharon Weston Broome, the mayor of Baton Rouge, said in a statement on Twitter that she was “deeply saddened” by the episode, noting that the officers were investigating the earlier slaying of a community member when they were shot.

“This is the call that no chief wants to get, no police officer wants to hear, an officer dying,” Paul said. “Not only were these police officers public servants. They are fathers, husbands, loved by the their families, and already dealing with the stress that we have to deal with this current COVID threat that we’re in. Still our heroes step up.”

John Bel Edwards, the governor of Louisiana, said on Twitter that it was “a dark day in our state.”