Police found the bodies in a home on the 2100 block of Ramsey Way, about 1 mile north of the 10 Freeway. According to the victims' older sister, April Mejia, the home was occupied by her mother, 52-year-old Manuela Padilla, her 17-year-old brother Juan Padilla and her 23-year-old sister Maryann Padilla.
Maryann Padilla's 28-year-old boyfriend also lived at the home, according to Pomona police. He is suspected in the killings, police said.
A relative called police shortly before 11 p.m., saying they received a call from the boyfriend. The relative said he threatened to harm everyone in the home, including himself.
The relative went to the home but could not get inside, prompting the call to police.
Mejia is in disbelief over the murders and says she can't believe her younger sister's boyfriend is the suspect.
"I really didn't think he would do anything like that. I knew he loved her and he didn't want to, you know, he said he couldn't live without her, but I never in a million years would have thought he would have taken my family," she said.
A motive is unknown, police said.
"It appears to be domestic-related, but we're not sure why the actual homicides occurred and why he killed himself," said Pomona police Lt. Mike Keltner.
The victims' family and friends say Maryann Padilla had been with the suspect for about four years. For the past several weeks, she had been trying to break up with him and get him to move out, family and friends said.
The family lived in the house for over 10 years. A neighbor said she did hear some loud noises overnight, but thought it was a crash on the freeway.
"This could have happened within 30 seconds, easily, from one room to the next room to the next, room, without anyone even knowing what had just happened," said Keltner.
Tearful family members gathered outside the home and neighbors remembered the hard working mother and her two children, now gone in a senseless crime.
"When you hear something like that you know, it's a tragedy, and right before Mother's Day," said neighbor Rosemarie Rogers. "It's sad."