Jenner was driving his Escalade and was towing a trailer with an all-terrain vehicle. The Escalade had front-end damage.
Jenner stayed on the scene and tried to help emergency personnel.
The driver of the white Lexus he hit was killed.
"He is really beat up over this and is in a complete state of shock," a family friend tells RadarOnline.com.
There were four cars involved in the accident. Jenner's Escalade, a Hummer, a Prius and a Lexus.
"He is traumatized right now because he is having the case of 'what ifs' and feels responsible for this poor woman's death," said a family friend.
Police are investigating what caused the accident and whether paparazzi, alcohol or texting played a role.
"As of right now, there is no indication that Bruce Jenner was being chased by paparazzi at the time of the crash," Los Angeles County Sheriff's Department Lt. John Lecrivain said. "There was a possibility that paparazzi was following him at the time of the crash, but that is a very regular occurrence, and (there is) no indication at this time it was a contributing factor of the crash."
"He did not appear intoxicated or under the influence of anything at the time," Los Angeles County Sheriff's Department Sgt. Philip Brooks said of Jenner.
Five people were hospitalized with minor injuries from the crash, according to the Sheriff's Department.