More details have been released about the horrific domestic violence deaths on Monday in Los Angeles, in which an infant girl was found dead on the 405 freeway and a 9-year-old was found injured on the shoulder.

Los Angeles Police detectives told KNBC that in the 8-month-old infant was in her older sister’s arms when their mother shoved them out of her SUV early Monday.

The baby girl was struck by at least one vehicle on the freeway, while the 9-year-old made her way to the shoulder with moderate injuries. She was taken to a hospital for treatment, as CrimeOnline reported.

The mother, identified as 34-year-old Danielle Cherakiyah Johnson, drove to Redondo Beach and slammed into a tree at a high rate of speed, killing herself.

The final link in the murderous chain came at Johnson’s apartment in Woodland Hills, where police found her boyfriend, 29-year-old Jaelen Chaney, stabbed to death with a kitchen knife.

Investigators initially said the infant was 5-6 months old but later learned she was a few months older.

Police told KABC that the 9-year-old witnessed Chaney’s murder and the death of her sister.

“We really don’t know why this incident escalated to such violence,” LAPD Lt. Guy Golan told KNBC.

Golan said there had been no calls to the apartment where the couple had lived for more than year.

“Looking at the history between the victim and suspect, they have been dating for a few years, but there’s no prior incidents of domestic violence reported between the two,” he said.

Police said the 9-year-old is in the custody of Child Protective Services.

They also said that Chaney’s family is devastated by the news, while Johnson’s family said they had been estranged from her for some time.

Police told KABC that Johnson was in the process of divorcing the 9-year-old’s father. They did not say if Chaney was the father of the baby.

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[Featured image: Redondo Beach crash site/KABC screenshot]