Police said 40-year-old James Fortney, of Temecula, is believed to have stabbed Kevin Rodriguez in an apparent case of road rage.
Rodriguez died at the scene in his girlfriend's arms, family members said.
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The young social media star's Instagram account has a following of more than 37,000. He listed his occupation there as a freelance videographer.
Riverside County Sheriff's Department deputies were called to the scene on a report of an assault around 12:15 p.m. in the 32200 block of Temecula Parkway. They found Rodriguez there with multiple stab wounds.
Rodriguez was transported to an area hospital and pronounced dead.
The assault was caught on camera by the suspect, according to the victim's family.
"He got his phone like this, he started recording it. And with the other hand, first he choked him. Kevin was trying to get away and that's when he got stabbed," said Kevin's father, Atticus Rodriguez.
It began on the street as an apparent road rage incident and the suspect followed Rodriguez and his girlfriend into the parking lot, where a confrontation started, family members said.
Then after the stabbing, the suspect appeared to realize what he had done and had a change of heart, according to family members.
"This guy was definitely in a rage for whatever reason," Atticus Rodriguez said. "When he realized what he did, he started helping him. Trying to bring him back to life. That was really weird. How do you do that to somebody, then realize what you did and try to help him? It makes no sense to me at all."
Fortney was booked at the Cois Byrd Detention Center on a charge of voluntary manslaughter.