At age 7, Robert Durst deliberately shoved his younger brother, Douglas, onto the ice at a skating rink, according to Douglas. He broke his wrist. That was their life, as boys and men: a low-grade menace that swelled as they grew up.

Now Douglas is 70, the leader of a small kingdom of Manhattan real estate; Robert, 71, went to court in New Orleans on Tuesday in handcuffs and an orange jumpsuit, with a smile bewildering to behold. A six-part HBO documentary, “The Jinx,” apparently led to his arrest over the weekend on charges that he murdered a close friend.

The climax of the series, broadcast on Sunday night, included a recording of Robert Durst apparently talking to himself in a bathroom: “What the hell did I do? Killed them all, of course.”

For much of the documentary, as Mr. Durst sparred with suspicions that he had killed three people — the friend, his first wife and a neighbor — he managed to deflect absolute certainty with a risky, engaging candor. Yes, he lied about what had happened the night his wife disappeared, but to get the police off his back. No, he didn’t tell the whole truth in a trial; nobody tells the whole truth.