Monday, Police Officer Quathisha Epps, 37, arrived at Manhattan Supreme Court to testify in a murder case in which she responded — both as a neighbor and an officer. One night two summers ago, she told the court, she heard gunfire outside her Eldridge St. apartment. According to a New York Post article by Laura Italiano, Epps placed the baby she was nursing in his crib, then told her three other kids to get into the bathtub. Then, she ran downstairs — barefoot and in her nightgown, carrying towels — to give a last moment’s comfort to Vincent Cruz, 17, who had been shot through the neck and would bleed to death in her arms. She said that, as she pressed the towels to his wounds, “I told him, ‘I’m here with you. … You’re very loved. Just hold on for me.’ ” As she cradled him, Epps called 911, while stretching out her leg to hold her toe against a knife on the ground — a piece of evidence. The next day, according to the Post, Epps realized she knew Cruz, who seven years earlier had tutored her son, then 3, in preschool. “This is a case that never leaves me,” said Epps, a community affairs officer at East Harlem’s P.S.A. 5. Ricardo Martinez is accused of shooting Cruz during an argument.