“When we told him to leave, he would just go to his car and sit in the parking lot and wait for us for hours,” Mr Handy said. “We called the police but they never showed up.” Police said they had no record of such calls for help. But in February 2020, surveillance images from the Islamic Center of New Mexico showed Mr. Syed slashing the tires of the car Mr. Hadi’s wife had parked outside the mosque there. Mosque leaders told Mr. Syed to stay away, and he did for months. Mr Syed is now charged with murder in the murders of Aftab Hussein and Muhammad Afzaal Hussain, and police said they were still gathering their cases in the other two murders. Afghan community leaders said they were relieved a suspect had been identified, but some were reluctant to attribute the killings to sectarian violence. The reasons for killing, they learned after decades of war, are often too complex to fit simple labels. Salim Anseri, a leader of the city’s Afghan community who knew Mr. Said and all the victims, is one of those not ready to judge. “Maybe he is mentally ill or had personal issues with the victims,” she said of Mr Syed. “From what I can tell, they were personal matters.” For Mr. Hadi, such distinctions matter little. Between bouts of tears, he said he still had trouble going back to where his brother’s life ended so abruptly. “I still see him every day when I come to work,” Mr Hadi said. “But he’s dead. Nothing is going to bring him back.” Susan C. Beachy and Kitty Bennett contributed to the research.