A California man allegedly walked up to a cop and confessed to murder — then led investigators to the bodies of two men in what prosecutors now fear could be the beginning of a serial-killing spree.

Marcelino Castro, 28, approached a San Jose police patrol officer around 5:14 p.m. Saturday and allegedly said he had killed someone.

His confession set off a grisly search through the city’s Guadalupe River corridor, where detectives ultimately discovered two bodies at separate locations — and raised the chilling possibility that there could be more victims.

“Although there’s only two victims it looks like the start of a possible serial killer case and I’m grateful he turned himself in before he continued,” Santa Clara County Deputy District Attorney Michael Gadeberg told the SFGATE.

The California Post has reached out to the Santa Clara County District Attorney’s Office for more information.

According to the police report, Castro described the first killing as involving a man he knew. The two went near Tamien Station to smoke methamphetamine, authorities said.

Castro allegedly then attacked him “without provocation,” strangling him and slitting his throat before concealing the body in a shallow grave near the Guadalupe River.

Investigators believe that death occurred Sept. 13.

Castro allegedly gave detectives information about another killing during questioning, leading them toward the area of Autumn Parkway and Coleman Avenue.

There, detectives discovered another deceased man.

The second alleged killing was markedly different, Castro told police he “lured” the victim toward the Guadalupe River Trail north of Coleman Avenue “to smoke,” according to the report.

Authorities say he then strangled the man and struck him with a rock before wrapping the body in a red tent and leaving it in tall grass.

That death is believed to have occurred Sept. 15 or 16, Gadeberg told SFGATE.

The identities of both victims remains unknown.

“Those areas are frequented by homeless people but our understanding is that the defendant lured them to those locations,” Gadeberg said.

The case has left investigators grappling with an apparent lack of an obvious connection between the victims.

Castro’s alleged motive remains under investigation, while authorities continue examining the circumstances surrounding both killings.

“It appears that this man may have just had a compulsion to kill and he started with someone he knew and then progressed to a random stranger,” Gadeberg said.

Castro was booked into the Santa Clara County Main Jail on two murder counts.

The killings are being investigated as San Jose’s 20th and 21st homicides of 2026.