A Salem man charged with domestic assault has died after being found unresponsive in a police station holding cell, prosecutors said. Hugh Kerr, 61, was charged with domestic assault and battery after his arrest Monday and placed in custody for the night, said Carrie Kimball Monahan, a spokeswoman for the Essex district attorney. At about 3:50 a.m. Tuesday, police found Kerr unresponsive during a routine check of the cells. He was taken to Salem Hospital, where he was pronounced dead, Monahan said. An autopsy will be performed by the state medical examiner, she said.