Inmate George Rosales, 18, who was in the medical ward attached to the Twin Towers jail, died early Thursday after being found in "medical distress" in a single-person cell, a spokeswoman said.
Rosales had been punched in the head by a deputy when he made a break for an elevator Tuesday, said Michael Gennaco, who heads the department's watchdog agency.
Nishida said it does not appear that the death was related to the altercation.
Gennaco, however, said it remains unclear what role the blow to the head played.
"There was a force incident two days prior. That's why the autopsy is important," Gennaco said.
Asked how high the level of concern was that the punch contributed to the death, Gennaco said that "at this point the concern is it needs to be looked at." He said that there was nothing to be done about determining the cause of death "until we find out from the pathologist how he died."
Sheriff's investigators haven't yet determined if the blow to the head was within departmental policy.
The death comes amid allegations of inmate abuse in the largest jail system in the nation. In recent weeks, firsthand accounts of brutality have surfaced from inmates, jailhouse volunteers and even a rookie deputy who resigned after he was allegedly forced to beat up a mentally disabled inmate. The FBI is investigating multiple reports of brutality and other deputy misconduct in the Los Angeles County jails.