LOS ANGELES (AP) — Police have linked three July stabbings of homeless people in the Los Angeles area to one suspect who left typewritten "death warrant" notes at each crime scene.

The third signed letter was found at a stabbing early Thursday morning in Hollywood and was similar to letters found at two previous stabbings in downtown and Santa Monica, Police Cmdr. Andrew Smith said. Police are asking for the public's help in finding a person of interest.

All three victims are in their 50s and were stabbed in the back in the early morning hours as they slept, Smith said. The victims survived, though one remains hospitalized, police said.

Police are warning homeless people to seek shelter at night and avoid sleeping alone in the streets.

"Any homeless person sleeping anywhere outside is vulnerable tonight — more vulnerable than usual," Smith said.

The attacks targeting the homeless are reminiscent of a series of stabbings in Orange County several months ago in which four people died. A suspect was arrested in those cases.

The first stabbing came July 3 in downtown Los Angeles, and is the only stabbing where a witness saw a suspect fleeing the scene, Smith said.

The Los Angeles Times reports that the victim crawled 100 yards looking for help with a large hunting knife lodged between his shoulder blades.

The second stabbing came Tuesday, when a man was stabbed as he slept on a bench in Santa Monica. A passerby responded to the victim's cry for help and called police, Sgt. Richard Lewis said.

The most recent stabbing on Thursday targeted a woman who was sleeping in the Hollywood area.

The letters left with the victims were all signed "David Ben Keyes," who police have named as a person of interest in their investigation, Smith said.

Smith emphasized that police are still unclear if the name on the death warrants is the name of the actual suspect, and police only want to question Keyes at this point.

Keyes may be homeless and is believed to be from the Santa Barbara area, Smith said.

Homicide Division Capt. Billy Hayes —whose detectives took over the case Thursday— said it was too soon to know if the crimes could be linked to the series of gory stabbing deaths of four homeless people in Orange County between Dec. 2011 and January.

Itzcoatl Ocampo, a former Marine, was charged in those homeless murders, and also has been charged with killing the mother and brother of his friend. Prosecutors say they will seek the death penalty in the ongoing case against Ocampo.