DES MOINES, Iowa — A white man with a history of racial provocations and confrontations with police ambushed and fatally shot two white officers in separate attacks as they sat in their patrol cars, authorities said.

Police took 46-year-old Scott Michael Greene into custody hours after the killings early Wednesday, less than three weeks after he argued with officers who removed him from a high school football game where he had unfurled a Confederate flag near black spectators.

Greene flagged down an Iowa Department of Natural Resources employee in a rural area west of Des Moines, identified himself and asked that the employee call 911. Sheriff’s deputies and state patrol officers took him into custody.

Green has not been formally charged, but he remained hospitalized Thursday for treatment of an existing condition, Des Moines police Sgt. Paul Parizek said. Police planned to provide an update on the case later in the day, he said.

Greene’s suspected in the early morning slayings of 24-year-old Justin Martin, who had been with the force in the Des Moines suburb of Urbandale since 2015, and 38-year-old Sgt. Anthony Beminio, who joined the Des Moines department in 2005.

Police responded to a report of shots fired shortly after 1 a.m. and found the Urbandale officer. Authorities from several agencies soon saturated the area. About 20 minutes later, they discovered the Des Moines officer, who had responded to the first shooting, Parizek said.

The shootings happened less than 2 miles apart, and both took place along main streets that cut through residential areas.

In the first shooting, investigators believe the gunman walked up to the officer’s car and fired more than two dozen rounds.

“I wouldn’t call it a confrontation,” Urbandale Police Chief Ross McCarty said. “I don’t think he may have even been aware that there was a gunman next to him.”

The shootings follow a spate of police killings in recent months, including ambushes of officers in Dallas and Baton Rouge, Louisiana. Five officers were killed July 7 in Dallas. Three more were killed later that month in Baton Rouge.

Race was an issue in those cases and others involving unarmed black men killed by officers. Greene is white, as were the officers.

Greene appeared to have issues with people of other races.

In the confrontation at the Urbandale High School football game, which Greene videotaped and posted on social media, he appeared to be trying to antagonize African-American fans when he shook a Confederate flag in front of them during the national anthem, McCarty said.

In the video, officers can be seen asking Greene to leave school property while he insists he was assaulted and his flag was stolen. He demands officers file theft and assault charges, saying someone hit his head and grabbed the flag.

In a back-and-forth with officers that lasts for nearly 11 minutes, officers say they could take a report but they cannot let Greene back inside the stadium because the school has banned him from the property. They also note they were returning his flag and ask if he purposely wanted to create a conflict by displaying it near African-Americans.

“I was peacefully protesting,” he responds. “That’s my constitutional right.”

The video ends with Greene promising not to “set foot on” school property and officers saying they will take down his information.