He was originally charged with vehicular manslaughter — but then detectives checked his internet search history.

A Michigan man purposely ran over a 64-year-old grandmother so he could have sex with her corpse, prosecutors have alleged.

Colby Martin, 29, had been originally charged with hit and run manslaughter and trying to conceal a body; investigators now claim he did much worse to it.

On September 20, retired nurse Melody Rohrer was reported missing by her husband from Hamilton Township, where she was last seen walking along County Road.

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Tracking her cell phone, detectives found it with Martin at a Walmart in Oshtemo Township, some 30 miles away; his 2013 Ford F-150 showed evidence of severe front end damage, detectives said.

The following day, Martin led them to Rohrer’s body at Three Rivers State Game Area. Police said he had struck her as she walked outside the Oak Shores Campground, before moving her body about 26 miles to the heavily wooded public park ABC13 reported. They said he had made multiple attempts to conceal several pieces of evidence.

He was charged that month with manslaughter with a motor vehicle, failure to stop at the scene of an accident resulting in death when at fault, and concealing the death of an individual. He was later released on a $300,000 bond.

But last week Martin was re-arrested — at his girlfriend’s house — on an open murder charge, after prosecutors claimed he had deliberately run over and killed Rohrer, with the intent of having sex with her dead body.

Detectives testified that they had discovered while sifting through Martin’s computer history that he had searched pornography involving dead or unconscious women immediately after Rohrer was reported missing.

Investigators also said they found used condoms in a trashcan outside his home, with both Martin and Rohrer’s DNA.

This time, Van Buren County District Court Judge Michael McKay denied bail.

“That is a very different set of facts,” he said.

“I think he represents the most extreme danger to the public. Chilling doesn’t begin to describe it.”

Martin’s attorney, Jim Mequio, disagreed with the judge, insisting the new allegations didn’t justify the upgraded murder charge.

“We’re still waiting for reports and more evidence from the prosecutor’s office,” he said. “From a legal standpoint, I’m not seeing the increase in charges will be justified.”

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