A tattoo more than a decade old on the calf of a Michigan State University health physicist accused of having sex with a dog might clear him of one felony charge.

A judge in the case against Joseph Hattey, 51 — who is accused of penetrating a basset hound with both his penis and his hands — continued a key hearing so additional testimony can be heard after Hattey’s attorney revealed that his client has a large tattoo on his right calf, the Lansing State Journal reports.

Attorney Patrick O’Keefe, who said he first learned of the ink Thursday, said the tattoo cannot be seen in photos that prosecutors say show the physicist recently penetrating the poor pooch. Hattey — who was placed on administrative leave from MSU’s Environment Health and Safety office after his arrest — said he can prove that he’s had the tattoo for about 15 years.

District Judge Thomas Boyd, who was considering whether to send Hattey to circuit court for trial, granted a continuance until July 5.

Earlier this month, the Michigan Attorney General’s Office approved an arrest warrant for Hattey on two counts of sodomy for committing a crime against nature, a bestiality accusation. Investigators said the incidents, which allegedly occurred between January and March, did not occur on MSU’s campus or with an animal owned by the university.

One criminal count against Hattey relates to testimony from an informant who claims the alleged sex acts happened earlier this year at Hattey’s home. The witness, who testified Thursday, had earlier told police that Hattey had genital contact with the dog and reached toward the animal’s anus before it ran away, court documents show.

The second count pertains to evidence found on a cellphone and laptop seized in March from Hattey’s home, an assistant state attorney general said Thursday. Two photos found on those devices show a man penetrating a dog, but the faces of neither the man nor the dog can be clearly seen.

Investigators claim the man in the photo has the “same general body type” as Hattey. The dog, meanwhile, has the “same distinctive fur pattern” as his pet basset hound.

But the photos do not show a tattoo on the man’s calf, where Hattey sports a large design, O’Keefe said.

Prosecutors argued there was enough evidence to send Hattey to trial, but Boyd disagreed with the claim that the tattoo was a “question of fact” to be left to a jury.

Hattey, whose creepy Craigslist ad seeking anyone with a “restless dog or horse” led authorities to him, faces up to 15 years in prison if convicted.

“Anyone have a restless dog or horse that needs occupied for a while?” the ad said, according to Ingham County Sheriff’s Detective Ryan Cramer.

“I love playing with them,” the user said. “Preferably not fixed but either is fine, male animals preferred.”