Local police have said the fatal shootings in the California town of Santa Barbara appear to be a "premeditated mass murder".
Seven people were killed, including the suspected gunman, and another seven injured during the attack near a University of California campus.
After reportedly spraying bullets from a moving car, the suspect was found dead, apparently with a gunshot wound to the head.
Speaking to reporters, Sheriff Bill Brown said: "We have obtained and are currently analysing videotaped evidence that suggests that this atrocity was a premeditated mass murder."
Mr Brown also indicated a possible connection between the killings and a YouTube video showing a young man promising a "day of retribution" against women who had rejected him.
More top news
Fine start to the week for most but turning wet and windy from Wednesday.
Thousands of people have lined the banks of the Mersey to see Cunard's three flagship ocean liners sail down the river.
Claims that surgeons used an old saw found in a cupboard to amputate a patient's leg are being investigated.