Phil Spector was found guilty in 2009 of second-degree murder in the death of actress Lana Clarkson — but Al Pacino and David Mamet, the director of Pacino’s new HBO film on the jailed music mogul, aren’t so sure about the verdict. While Mamet believes Spector’s not guilty, Pacino says he “was left with an ambivalence; there’s no doubt about that.” “David thinks he’s not guilty, but the movie takes a cryptic approach,” Pacino says in the latest issue of Rolling Stone, out Friday. “You’re wondering if it was an accident. I like the fact that it’s a bit up in the air.” Pacino’s expected at a VIP screening of “Phil Spector” tonight at Time Warner Center along with Barry Levinson and Jeffrey Tambor.