As in all the truly great tellings of murder mysteries, David France’s “The Death and Life of Marsha P. Johnson” is far more interested in the why than the how or who, and when police don’t necessarily even consider the case to be a murder investigation, the question of why extends even further. What can be certain is that in 1992, Johnson, an iconic LGBT activist, was found dead off the Christopher St. Pier in New York, and having endured every possible sling and arrow that life could throw at a person in fighting for equality, it stands to reason the transgender woman wasn’t one to even consider taking her own life.

Like France’s previous film, “How to Survive a Plague,” the electrifying chronicle of activism by the gay community that fought back the AIDS crisis, his latest exists in the present tense while telling a story from the past, simultaneously relaying Johnson’s considerable legacy, personally taking in transgendered teens off the streets of New York and inspiring others to do the same while becoming a primary voice for the transgendered in the LGBT movement, while one of those she helped indirectly, Victoria Cruz, pursues her case 25 years after it has gone cold as part of the New York City Anti-Violence Project. A former model who sacrificed none of her fierceness after being kicked off the catwalk when it was discovered she’s transgendered, Cruz’s dogged investigation leads her all across New York state, into dimly lit bars and homes with reticent interviewees that give the film a real Raymond Chandler feel. But with France’s own detective work, you’re taken right back to the events leading up to Johnson’s death and the fervor it created just after through choice archival material that captures the cultural moment perfectly.

Given the title, it’s slightly surprising, but entirely understandable once “The Death and Life of Marsha P. Johnson” starts unfolding that Johnson is left as a slightly enigmatic figure in the way that the victim of an unsolved murder can never have their story told, though France’s and editor Tyler Walk’s judicious reveals of footage of her throughout the film makes you keenly aware of what’s been lost and her influence is legion. But shrewdly, the real face of the film becomes Sylvia Rivera, who met Johnson when she was 12 and considered her a mother as the two grew close as trans activists. Rivera, a boisterous personality is as engaging as they come, but she’s particularly compelling in representing the transgender community’s place unfairly as the stepchild of the LGBT movement as you see her at rallies being booed by those who are ostensibly fighting for the same principles she is and know what it’s like to be marginalized. That this attitude continues to linger over Cruz’s investigation is infuriating, but in how clean a line France makes from one era to another, it becomes undeniable.

Bryce Dessner’s stirring score and cinematographers Thomas Bergmann and Adam Uhl’s ability to capture the whole histories of the film’s subjects in composing shots that take advantage of the ambiance contribute to the immediacy and contextual richness of “The Death and Life of Marsha P. Johnson,” but it’s especially dynamic because of how France can pluck the most important and telling moments out of archival materials like they were his most vivid memories and draw out his subjects in the present day from years of being an investigative reporter, evident generally in his journalistic rigor tempered with great compassion. In telling Johnson’s story, he keeps her memory alive, which is no small thing to say, and whether or not he and Cruz can help bring her justice through the legal system, there’s no doubt “The Death and Life of Marsha P. Johnson” does right by her.

“The Death and Life of Marsha P. Johnson” does not yet have U.S. distribution. It will play at the Tribeca Film Festival on April 23rd at 9 pm at the Regal Battery Park Cinemas and April 28th at the Cinepolis Chelsea at 6:30 pm.