"I didn't even know he had a knife until I saw him put his hand up," he said.
Police say the incident started as a domestic argument. The suspect went to his ex-wife's home Thursday morning and got into a violent dispute.
"The mother-in-law, we believe, tried to intervene and was also attacked and succumbed to her injuries at the scene," LAPD Lt. Ted Matthews said.
The body of his mother-in-law was found in the street near the house. The knife he used was just a few feet away.
Police say the suspect left and went to the Colorado Blvd Bridge in Pasadena near the Rose Bowl. There, he jumped to his death.
Detectives confirmed there was a restraining order on file for the man.
Neighbors said they never heard any arguments between the couple, but were aware of the restraining order.
Police are still investigating the killer's motive.
There were reports that the suspect may have been heading to his son's school.
"School police assisted us and we immediately took the child into protective custody, because at the point we did not know where the suspect was," Lt. Matthews said.
The 6-year-old boy was taken by police and is now safe with relatives.