Police and fire units went to the Islander Motel at 4101 Mowry Ave. after a woman was found unresponsive by a friend in one of the rooms, according to Fremont police.
The woman, a 41-year-old transient from Fremont, was declared dead at the motel.
An autopsy revealed she had sustained trauma to the head, but investigators were unable to determine how or where the trauma happened.
Investigators are looking for witnesses that may have seen a woman being carried from the motel parking lot into a room by one or more male subjects.
One of the subjects is described as a Hispanic man with slicked back wavy hair curled at the neck, between 24 and 26 years old, 5 feet 10 inches to 6 feet tall and weighing around 150 pounds.
Anyone that may have witnessed anything pertaining to the case is asked to call the Fremont Police Department investigative unit at (510) 790-6900.