A California father has been arrested in the decades-old killings of five of his infant children, a case the sheriff said had haunted his agency for years.

Paul Perez, 57, was arrested at a state prison in Delano, days before he was expected to be released on unrelated charges. He is suspected in the deaths of the children born between 1992 and 2001.

The case reflects an “unspeakable evil,” Yolo County Sheriff Tom Lopez said.

“I cannot think of a case more disturbing than this one,” he said. “There can be no victim more vulnerable and innocent than an infant and unfortunately this case involves five of them.”

Authorities started investigating after the decomposed remains of the child recently identified as 3-month-old Nikko Lee Perez were found in 2007 in a sealed, submerged box in an irrigation slough near Woodland, California, about 80 miles northeast of San Francisco.

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An autopsy found he died of blunt force trauma.

The remains were identified in October after authorities used an expanded DNA database that they had not used before on the cold case. State department of justice officials previously had been checking a more limited DNA database weekly for direct matches.

Mr Perez is charged with five counts of premeditated murder with special circumstances of lying in wait, torture and multiple victims. He also faces charges for assault on a child under 8 for the same victims and criminal enhancements for his prior convictions.

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District Attorney Jeff Reisig said Mr Perez was eligible for the death penalty but he has not yet decided whether to pursue it. He is scheduled to be arraigned on Tuesday.

“The investigation in this case uncovered a deeply disturbing and chilling case of infanticide,” Mr Reisig said.

Officials declined to say whether Mr Perez has other children or family members, or whether all the babies have the same mother.

They asked for witnesses who know Mr Perez or the children to come forward. The remains of three of the children have not been found.

Nikko’s body was found on March 29, 2007, in an irrigation canal popular with anglers looking for carp or catfish. Fisherman Brian Roller told reporters at the time that he shot an arrow into the murky water and it struck a box buried under the mud. When he hauled it out of the water and opened it, he found stones and pieces of metal used to weigh it down. The baby´s badly decomposed body wrapped in a blanket.

Authorities said a decomposed diaper was also in the box, indicating the infant, who was born in 1996, had been cared for at some point.

Investigators immediately treated the case as a homicide and submitted the baby´s DNA to the US department of justice in hopes of obtaining an identity. They also enlisted the help of a forensic anthropologist, who determined the remains were those of a boy about one month old who died of blunt force trauma.