One knife was found and marked as evidence on the front sidewalk, and another, longer knife was being examined closer to the front door of the home.
Police aren't confirming whether either one was used in the fatal stabbing inside the home.
Neighbors who rushed in to help Tuesday morning say it was a terrible scene.
"It was a horrific scene to go in there and see what we saw," said neighbor John Sennett.
Sennett lives across the street. He was awakened by a woman screaming around 3:30 a.m.
"Me, my wife and my son ran out here right away, and she was over there just screaming," said Sennett.
That's when he and three other neighbors ran inside to help. They came across the suspect, who appeared to be a teenager.
"Ran into the house, and that's where I see the father holding the boy down as the boy was hitting him and smiling, just beating him," said Sherry Hicks, a family friend.
Police say the suspect is 19-year-old William Gary Simpson Jr. They say he fatally stabbed an 18-year-old woman, and also stabbed her father and one of her friends. The father, 49, and the friend, 17, were hospitalized in critical but stable condition. Police did not identify the victims.
There was another person inside, the mother, who was the one who came outside screaming. She was unharmed.
"We're still investigating to determine a motive of why the suspect ended up stabbing this girl," said Murrieta Police Captain Dennis Vrooman.
Neighbors say the suspect was an old family friend who had actually lived there for quite some time. But they say he left about a year ago when he refused to pay rent to the homeowner, who had apparently given him a number of chances, but ended up kicking him out.
"She did the best she could, and for him to turn around and do this, really, I can't understand that," said Sherry Hicks.
Police say it does not appear to have been a robbery.
If you have information related to the case, contact Murrieta Police at (951) 696-3615, or Detective Danny Martin (951) 461-6340, or Sgt. Phil Gomez (951) 461-6356. If you wish to remain anonymous you are encouraged to call We-Tip immediately at (800) 782-7463.