The U.S. Immigration and Customs Enforcement officer who allegedly fatally shot a Colombian man in Maine on Monday was prone to violence and held racist beliefs, according to some of the people who were close to him.

Ashley Brouillette told NPR her ex-husband, David Brouillette, was the officer who fatally shot Joan Durán Guerrero four times during an attempted traffic stop in Biddeford, Maine, on Monday. She said she found out he was the officer responsible when he called her on Wednesday, asking her to vouch for his character.

“He asked me to basically talk good in his character, not to talk bad about him. And if I couldn’t not talk bad about him, then just not to talk at all to anybody,” she told NPR. “And I told him that I was not going to lie for him. He asked me not to talk about the abuse in our marriage. And I told him again I was not going to lie for him.”

David Brouillette did not respond to messages from NPR seeking comment. An ICE spokesperson said the agency will not confirm or deny whether Brouillette was the ICE officer responsible for Durán Guerrero’s death. ICE spokesperson Lauren Bis did say in an email that the ICE officer in question has “nearly a decade of federal law enforcement experience with required training.”

Scott Collins told NPR that he was best friends with David Brouillette in high school in Maine. Collins testified on behalf of Ashley Brouillette in the divorce proceedings. David’s attorneys said that Collins and David “were once friends, but their relationship ended because Mr. Collins was jealous of Mr. Brouillette’s successful career.”

“He had a bad tendency of going out and looking for fights,” Collins said. “If he saw something online that he didn’t like, that somebody said that he knew, he would go out and start that fight.”

Collins also said that David Brouillette used anti-Black racial slurs in high school. Ashley Brouillette says she worries racism may have played a part in Durán Guerrero’s death.

“He has displayed racism. His nickname in high school was ‘White Boy David,’ if that tells you anything,” she said.