There’s a contradiction built into the phrase “true crime”: Most of that booming genre’s most popular works depend, for their effect, on the unknowability of the truth. It may be strongly suspected or widely assumed, but its elusiveness makes possible the combination of investigation and outrage that draws us in. If you want a satisfying resolution, you’re better off watching crime fiction.

Fans of the genre’s higher end — where time, budget and attention to detail produce something better than reality-television filler — are currently in luck. HBO has dedicated three weeks of its documentary schedule to a trio of two-part crime stories, “I Love You, Now Die,” “Behind Closed Doors” and “Who Killed Garrett Phillips?” (The first two are on HBO Go and HBO Now, having already aired on cable; the third airs Tuesday and Wednesday ). Though none are at the level of “The Jinx” or “Mind of a Murderer,” all are solid and absorbing.

And just over the horizon, beginning Aug. 1 on Sundance TV, is “No One Saw a Thing,” a six-part immersion in rural Missouri and the notorious 1981 vigilante killing of Ken Rex McElroy.

Each of the four hinges on a mystery, but the questions vary widely. “Behind Closed Doors,” about the 2008 murders of a teenage girl and a domestic in an apartment near Delhi, and “Who Killed Garrett Phillips?,” about the 2011 killing of a young boy in his upstate New York home, are classic locked-room stories and straight-ahead whodunits. In each case, suspects — the girl’s parents, the boy’s mother’s former boyfriend — were indicted and brought to trial under intense media scrutiny, but both cases remain unsolved.