DALLAS — Five Dallas police officers were killed and six others were wounded by snipers on Thursday night during a demonstration protesting shootings by officers in Minnesota and Louisiana this week, the Dallas police said.

The police believe four suspects coordinated the attack with rifles, Police Chief David O. Brown said, and positioned themselves in triangulated locations near the end of the route the protesters planned to take. The police had three people in custody and were negotiating in the early-morning hours with a fourth, who was in a garage in downtown Dallas at El Centro, a community college.

That suspect had exchanged gunfire with the police and was being uncooperative in talks, Chief Brown said at a news conference in the lobby of City Hall.

The suspect “has told our negotiators that the end is coming and he’s going to hurt and kill more of us, meaning law enforcement, and that there are bombs all over the place in this garage and downtown,” Chief Brown said.

“We are being very careful in our tactics so that we don’t injure or put any of our officers in harm’s way, including the citizens of Dallas, as we negotiate further,” he added.

The three other suspects are a woman who was taken from the garage and two others who were taken in for questioning after a traffic stop.

Chief Brown said the suspects in custody were not providing investigators with many details. “We just are not getting the cooperation we’d like, to know that answer of why, the motivation, who they are,” he said.