NEW You can now listen to Fox News articles! A tip in the search for missing man Keith Palumbo led investigators to a cemetery crypt — and a gruesome discovery inside. The haunting case of the 36-year-old Delaware County, Pennsylvania, musician and tattoo artist, who was murdered by his longtime friend, is now the focus of Oxygen’s true-crime series, "Philly Homicide," where retired detective Chris McMullin revisits some of the city’s most explosive crimes. "This is a very sad case," McMullin told Fox News Digital. "Through a very thorough investigation involving interviews with other parties that either had knowledge or some type of involvement, it led them to Mount Moriah Cemetery. And honestly, it was not that surprising to me because I know that a lot of stolen cars have been dumped there." FORMER UNDERCOVER AGENT RECALLS INFILTRATING THE HELLS ANGELS: 'A DANGEROUS GAME TO PLAY' Keith Palumbo, a heavy metal guitarist, was murdered in February 2020.…