DES MOINES, Iowa >> Police say a white man with a history of racial provocations and confrontations with police has ambushed and fatally shot two white officers in separate attacks as they sat in their patrol cars.

Police took 46-year-old Scott Michael Greene into custody hours after the killings and 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. The officers were fatally shot early Wednesday.

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.