Jack Black, whose career was built on getting deep inside the skin of his characters, arguably reaches the pinnacle of his performances as Bernie Tiede in “Bernie” — based on actual events that happened in small-town Texas 17 years ago.

Directed by Richard Linklater (Black’s second team-up with him since “The School of Rock” in 2003), “Bernie” is a fictional documentary, sticking to the bare facts while speculating on unrevealed emotional agendas. The story of a mortician who took up with a wealthy, decades-older local widow and was later accused of killing her in cold blood, “Bernie” is by turns sinister, funny and very sad. The trial made headlines in the United States before it was forgotten. According to the film, though, locals still talk about it as if it happened yesterday.

Bernie was in his late 30s and single, the most popular man and assistant funeral director in a town whose demographics were dominated by about-to-die old men and about-to-be-widowed “DLOL (Dear Little Old Ladies).” Bernie, an out-of-state transfer with a mortician’s degree, was an immediate hit. Everyone loved him. In an interview with The Japan Times, Black gave his own description of Bernie (he had visited the man in prison before Linklater started shooting the film): “Bernie is this very personable and charismatic guy. He wasn’t the big and loud kind of charismatic, actually he’s very, very shy. But there’s a magnetism to him and he has a knack for getting people to like him in an easy-going way. Richard and I thought he would be great movie material. Not many movies are made about likable murderers and Bernie is just the sweetest, most pleasant guy anyone could hope to meet. There was just this one horrible incident in his life among all the nice-ness and I thought that was very compelling.”

What happened was this: Bernie took it upon himself to offer a mega dose of TLC to the town’s most hated woman, Marjorie Nugent (played by Shirley MacLaine with total conviction), after the death of her husband. In the movie, one DLOL says derisively: “Some people would have killed Marjorie Nugent for five dollars!” — which sums up local sentiment toward the recently widowed, flithy-rich and legendary bully of a woman.

“I had a lot of opportunities to study Bernie,” says Black. “There were so many videotapes of him directing funerals, singing at church services, performing in theater productions … he was everywhere! I also got to talk to him and get a sense of what he’s like. But regarding Marjorie, there was nothing much to go on. She was more or less a recluse and no one really knew her well. I gathered though, that though she was extremely unpleasant. Shirley MacLaine said she didn’t want to play her like Nurse Ratched (“One Flew Over the Cuckoo’s Nest”) but as someone with more depth and dimension. Marjorie wasn’t satisfied to be just a DLOL. She wanted to be someone special, especially to Bernie. She was vulnerable like that.”

For a while, Marjorie did manage to monopolize Bernie’s time. “At first, she wouldn’t give in to Bernie’s charm,” says Black. “But he persisted, and she caved in. For Bernie, Marjorie Nugent was a challenge, and he probably said to himself, ‘I’m going to crack this nut.’ Because he had an enormous need to be liked by people. That’s just the way he was. He would give people money and gifts and do them huge favors and dedicate his life to making others happy. Marjorie didn’t capitulate so easily and he couldn’t let that go. He had to make her like him, to bring her to a point where she couldn’t live without him.”

The question of whether Bernie and the 81-year-old Marjorie were lovers is one of the undercurrents running through the story — but Black says their relations were psychological rather than physical. “They had a codependency thing going,” he says. “Typical of many abusive relationships. Bernie needed Marjorie because her financial situation made it possible for him to give money and presents to the townspeople. He loved doing that, and didn’t want to give that up. And Marjorie needed him, as a nice young fellow to bring along on trips and go to spas together and all that. At the same time, she resented that he was so nice, not just to her but everyone. In her mind, no one could be that nice, and well, in the end she was proved right.”

Indeed, Bernie functioned as slave, boyfriend and butler, and not necessarily in that order. When they went to spas together, they were massaged together side by side, hands clasped together like a long-term couple. At home, Bernie did her laundry and folded her voluminous panties. He took care of her bank account, took her to restaurants and put up with her tantrums. Marjorie’s own family kept a healthy distance from her but Bernie was there for her, more or less 24-7. “I wondered a bit why he just didn’t walk away,” Black says. “She didn’t lock him up or anything, and he had his own house. But I think toxic relationships tend to be like that. It’s never easy, and it’s never simple. Bernie probably thought he could change her, that some of his sweetness would rub off on her. But before that could happen, he himself reached his own breaking point. He was a pressure cooker just waiting to explode.”