PHILADELPHIA—A Philadelphia man was freed from prison Tuesday after 37 years in a case marred by detectives who allegedly offered a witness sex and drugs at police headquarters in 1983 in exchange for false testimony. The trial witness was charged with perjury just days after Willie Stokes was convicted of murder in 1984. But Stokes didn’t learn about that perjury plea until 2015, decades into a life sentence. Stokes, 61, walked out of a state prison near Philadelphia eager to get a hug from his mother and a corned beef hoagie. His mother was too nervous to come after several earlier disappointments, so he greeted other family members instead. “Today is a tremendous day. We’re all very thankful,” said his lawyer, Michael Diamondstein. “However, it’s also a sad day, because it reminds us of how lawless, unfair and unjust Philadelphia law enforcement was for so long.” Both detectives who allegedly …