Joe McGinniss made his name writing about a murder case. His 1983 book, “Fatal Vision,’’ about US Army doctor Jeffrey MacDonald, who was convicted of killing his pregnant wife and two daughters, was a monumental bestseller and made McGinniss something of a celebrity. So we were intrigued to learn that McGinniss is back in a courtroom, this time in western Massachusetts, covering the trial of Cara Lee Rintala, who’s charged with first-degree murder in the strangulation death of her wife, Annamarie Cochrane Rintala. (Just underway in Northampton, it’s the Bay State’s first murder trial in which the victim and suspect are same-sex spouses.) How do we know McGinniss is writing about the case? Because he said so on Facebook. McGinniss, never accused of being shy, not only revealed that he’s covering the trial for Boston magazine, he’s also posting pictures and testimony. “You wouldn’t expect memorable similes from a fingerprint expert employed by the Massachusetts State Police,’’ McGinniss wrote this week. “But a 17-year veteran named Christopher Dolan informed us today that ‘Getting a fingerprint off a dead body would be like getting a fingerprint off a pancake.’’’ Asked Thursday if he’s scooping himself, McGinniss said no. “These are just amusing little snippets,’’ he said. “I think to some degree, I’m actually attracting a little bit more attention, which will mean Boston magazine won’t be publishing into a vacuum.’’ If you’re wondering whether the editor of Boston magazine is happy with his correspondent writing about the trial on Facebook, he isn’t. BoMag editor John Wolfson confirmed he hired McGinniss to cover the trial, but, after an audible sigh, he declined to comment on the postings. Next thing we knew, McGinniss updated his Facebook status to say he’d no longer be writing about the trial on Facebook: “Sorry to say that my editors at Boston Magazine have requested that I stop posting updates on the Rintala trial. They are paying me and Facebook isn’t, so you’ll hear no more from me about it until my story appears in the June issue.’’ Darn. Now, we’ll have to buy the magazine.