Brian Diez, 26, allegedly then drove to a house on the 1200 block of Rue Way in Rancho Cucamonga where he was found dead with what appeared to be a self-inflicted gunshot wound.
Authorities said they found his 4-year-old daughter and 13-month-old son unharmed and with Diez's sister and other family members at the home.
Police found four victims dead at the scene:
- Deborah Langstaff, 23, the mother of Diez's kids.
- Primo Verdone, 24.
- Russell Nyland, 42.
- Ashley Nyland, 20.
Brock Kelson, 20, and Deborah Nyland, 44, were transported to Havasu Regional Medical Center. Kelson succumbed to his injuries and died at the hospital. Nyland was transported to Sunrise Medical Center in Las Vegas.
"I guess they broke up and she had another boyfriend," said Keith Hotman, a neighbor of the Lake Havasu home. "I guess he came back last night and decided he was going to take them all out while they were partying."
Neighbors in Rancho Cucamonga said they remember seeing Diez on visits.
"Every once in a while he would stop by for a weekend to hang out with his sister," Stump said. "I knew he had a child the same as our daughter."
Investigators said Langstaff took out a restraining order against Diez earlier this year to keep him away from her and the children. Diez was arrested about two weeks ago for violating that restraining order and that may have triggered the shooting.