A man who’d been missing for a week was mysteriously found fatally shot alongside his pal inside a Long Island home — with cops saying the double slay appears to be drug-related, they said Wednesday.

Suffolk County detectives were investigating the disappearance of Ian Saalfield, 45 — who was reported missing by his wife on April 26 — when they showed up at a home on Hollywood Avenue near South Evergreen Drive in Selden around 10:45 p.m. Tuesday, cops said. 

Inside, they found the bodies of Saalfield, of Lake Grove, as well as Robert Julian, 58 — who lives at the home, authorities said. 

Both had been shot and were pronounced dead on scene by a physician’s assistant from the Suffolk County Medical Examiner’s office, cops said. 

Their relationship is unknown, but investigators believe they were friends, according to police.

Court records show that Saalfield served time in prison in North Carolina in the 1990s and in New York for criminal sale of a controlled substance.

One neighbor said Thursday that Julian had struggled with drug abuse.

“Bobby was a friendly, social guy, but he had a real dark side,” the neighbor, who asked not to be identified, told The Post. “He had a serious drinking and drug problem. Very bad. The drug problem was serious. He was a crazy dude.”

Nonetheless, Julian had also volunteered at a local food pantry for the past 10 years — and was there on Monday, pantry workers said. 

“That’s the last we saw of him,” Susan, who runs the program, said Thursday. “We have no idea what happened. We’re all in shock. It’s terrible.”

Detectives are looking into the possibility that the double-slaying was drug-related, cops said.

No arrests have been made and no suspects were immediately identified.