IN a monstrous twist to a horrendous crime, Aruban police now believe that miss­ing Maryland beauty ROBYN GARDNER was buried alive.

The ENQUIRER has learned ex­clusively that authorities received an anonymous but credible phone tip that the blonde beauty was buried – while still breathing – in a dog’s grave.

The informant’s sensational lead triggered a massive search of the Dog Graves Beach area of the Caribbean island, hoping to find evidence to nail the man of­ficials are convinced killed Robyn – Maryland technology expert Gary Giordano.

During the week-long search, specially-trained dogs indicated several possible spots where a body might be buried, and police plan to follow up with a thorough investigation of those areas.

Robyn, 35, who met Giordano, 50, through an online “swingers sex” site, was vacationing with him on the posh Caribbean resort island. But on Aug. 2, Giordano told police that the pair had gone snorkeling and Robyn never made it back to shore.

Police didn’t buy his story, espe­cially after he rushed to collect on a $1.5 million insurance policy he had taken out on Robyn just two days after she went missing.

Sources told The ENQUIRER that police believe the telephone tip may have come from a mysterious strang­er – a heavily tattooed white Ameri­can in his 40s with dark, curly hair. Cops initially believed he was an ac­complice of Giordano’s in a murder-for-money scheme.

“The tipster told cops he believed that Giordano thought he had beat­en and suffocated Robyn to death dur­ing a struggle,” re­vealed an insider.

“He secured her arms and legs with duct tape and taped a plastic bag over her head before driving to Dog Graves Beach. There, he dug up a fresh dog’s grave with his hands, removed the dog’s body, widened the hole and put Robyn in it. He placed the dog’s body on top of hers – and covered them up.

“The chilling part is that the caller told cops Robyn started moaning and moving when Giordano filled in the hole – burying her alive!”

The pretty victim was too weak from the beating she had suf­fered and from suffocating inside the plastic bag to defend herself.

After allegedly cleaning himself up at the water’s edge, Giordano stopped at a restaurant and asked employees to call the cops, accord­ing to the insider.

“Police believe the caller’s story makes sense. Giordano had scratches on his throat which looked like they had been put there by a woman’s fingernails. His shoes were wet but his clothes were not, leading police to believe he had briefly walked into the water to clean up.

Dog Graves Beach is an eerie spot on Aruba, holding the graves of more than 1,000 pets. The soil is mostly sand and could easily be dug by hand. Six dogs – which can tell the difference between a human and canine corpse – were brought in from Holland to search the vicinity.

Giordano is being held by authorities but is refusing to cooperate.