Police in Orange County said on Monday they do not believe that a transient found dead on Monday was the fourth victim of a suspected serial killer operating in the area.

The body of an unidentified homeless man was discovered at mid-morning in Santa Ana near the truck where he was apparently living, police said.

Blood was also found in the truck, which was parked behind a tire store.

Santa Ana Police Cmdr. Tammy Franks said an autopsy was being conducted to determine how the man died but that the case did not appear to be a homicide.

We're not thinking it's a homicide, but we haven't ruled it out until they do the autopsy, Franks said.

Authorities are searching for a suspected serial killer described as a thin man between the ages of 18 and 25 who they believe may be responsible for the stabbing murders of three homeless men in December.

The killings have put Southern California homeless and their support groups on edge and prompted efforts by Orange County Rescue Mission workers to move the homeless into shelters and counsel them about protecting themselves.

On December 30, a 57-year-old transient was found stabbed to death at the bottom of a stairwell outside a library in Yorba Linda.

Two days earlier, a 42-year-old homeless man was discovered slain in a similar fashion on a bike trail in Anaheim.

And on December 20, a 53-year-old transient was found stabbed dead at a shopping center in the city of Placentia.

We believe these murders are likely committed by the same suspect and we feel he is extremely dangerous to the public, Anaheim police Chief John Welter told reporters over the weekend.

Police say they have surveillance video of the killer from the shopping center slaying and that footage shows he was waiting for the victim.