Though the exact cause of death has not been officially declared, the homeless man, described only as a man in his 50s, was found covered in blood next to the Yorba Linda Library.
On Wednesday, a homeless man was found dead with multiple stab wounds along the Santa Ana River trail in Anaheim.
On Dec. 21, a 53-year-old transient was found dead outside a strip mall in Placentia. Officials say he was violently stabbed to death where he often slept.
Investigators from Anaheim and Placentia are joining Brea police to see if the three killings are the work of one suspect.
The identity of the victims have not yet been released.
"That's just crazy, it blows me away," said Yorba Linda resident Rod Collins. "These people have problems enough. Now they have to worry about somebody trying to kill them for apparently no reason."
Anyone with information is urged to call the Brea Police Department at (714) 990-7624.