Authorities in Massachusetts are investigating whether a man who killed two people in the Boston suburb of Winthrop on Saturday targeted them because they were Black, after officials found “troubling white supremacist rhetoric” in the gunman’s handwriting, a prosecutor said. The Suffolk county district attorney, Rachael Rollins, identified the gunman as 28-year-old Nathan Allen and said investigators uncovered writings that expressed “antisemitic and racist statements against Black individuals”. Authorities said Allen shot and killed David Green, a retired Massachusetts state police trooper, and Romana Cooper, a US air force veteran, after crashing a stolen truck into a building on Saturday afternoon. Officials described the two victims as innocent bystanders. Allen was fatally shot by police moments later. The gunman “walked by several other people that were not Black and they are alive”, Rollins told reporters on Sunday. “They were not harmed. They are alive and these two visible people of color are not. We will continue to look and see.” Rollins did not provide more details about the writings or where they were found. She cautioned that the investigation was in its early stages but said: “These families deserve answers and we will find out what happened here.” Green worked in law enforcement for nearly 40 years and retired in 2016, said Christopher Mason of Massachusetts state police. Green was shot outside his home, Mason said. “Trooper Green was widely respected and well-liked by his fellow troopers, several of whom yesterday described him as a ‘true gentleman’ and always courteous to the public and meticulous in his duties,” Mason said in a statement. “From what we learned yesterday, he was held in equally high regard by his neighbors and friends in Winthrop.” State police said officials were investigating whether Green “may have been trying to engage the suspect to end the threat”. On Sunday, mourners gathered and some left flowers near the destroyed building, the Boston Globe reported. Brian Marks, who owns the building, told the Globe he was in “utter shock”. “I rushed down and came to what, to me, looked like something out of a movie or something,” he said. Bob Harrington, who lives nearby, said he heard loud crashes, saw a man get out of the truck and walk down the street and then heard gunshots. He then saw a woman lying on the ground, he said.