A depraved California dad has been charged with killing his five infant children over the course of a decade in a cold case that “haunted” investigators for years, police said Monday.

Paul Perez, 57 — who had been serving time at a prison outside Bakersfield, Calif., for unrelated crimes — was arrested Thursday after detectives made a gruesome connection between a dead body from 2007 and its four dead siblings, Yolo County Sheriff Tom Lopez said, according to BuzzFeed News.

“While I am proud of the efforts of my investigators and coroner’s office, this is not a day that will bring joy to any one of us. In my 40 years in law enforcement, I cannot think of a case more disturbing than this one,” Lopez said in a statement.

“There can be no victim more vulnerable and innocent than an infant, and unfortunately this case involves five.”

Perez was arrested on the new charges at Kern Valley State Prison just four days before he was scheduled to be released.

The cold case began in 2007 when the body of a dead baby was found by a fisherman in a waterway east of Woodland, the sheriff’s office said in a news release.

Those decomposed remains had been in a sealed container, weighed down in the water by heavy objects, police said.

Officials gathered the infant’s genetic profile and uploaded it into the FBI’s criminal justice DNA database. But for years, no matches ever came and the case went cold, BuzzFeed News reported.

The case “haunted” the sheriff’s office as they tried desperately to figure out who the baby was, Lopez said, according to BuzzFeed News.

Using new DNA techniques, police were finally able to get their answer in October 2019 when they determined the child was Nikko Lee Perez, born in Fresno in November 1996, cops said.

With that information, investigators were able to determine baby Nikko had siblings — and each one of them was also presumed to be dead.

Police identified the children as Kato Allen Perez, born in 1992; Mika Alena Perez, born in 1995; a second Nikko Lee Perez, born in 1997; and finally, Kato Krow Perez, born in 2001.

The remains of the last three children have not yet been located. Baby Kato was already known to police to be dead.

“The allegations announced today are heartbreaking. There is absolutely no place in our society for horrendous crimes against children,” California Attorney General Xavier Becerra said in a statement.

“At the California Department of Justice, we will do everything in our power to track down criminals who think they have evaded the grip of justice.”

Officials are still in the process of building a complete case against Paul Perez, but he’s facing five counts of first-degree premeditated murder, Yolo County District Attorney Jeff Reisig said, according to BuzzFeed News.

The prosecutor added Paul Perez is suspected of committing the killings by “lying in wait” and “through torture,” the outlet said.

The means and motive behind the babies’ deaths have yet to be disclosed.

Paul Perez is scheduled to be arraigned Tuesday and, if convicted, he could face the death penalty, according to BuzzFeed News.