“The Backyardigans” (9 a.m., Nickelodeon): A high-seas adventure takes Uniqua, Austin,

“The Backyardigans” (9 a.m., Nickelodeon): A high-seas adventure takes Uniqua, Austin, Tasha and Pablo to Camp Walk-a-Planka. The half-hour special kicks off a pirate-themed week, which includes a Wonder Pets’ “Save the Pirate Parrot” episode at 10 a.m.

“RFK Must Die: The Assassination of Bobby Kennedy” (8 p.m., the Documentary Channel): Who shot Robert Kennedy? On the 40th anniversary of his death, the Documentary Channel airs “RFK Must Die: The Assassination of Bobby Kennedy,” the result of an investigation into still-unsettled questions surrounding his assassination on June 5, 1968, as he campaigned for the White House. BBC filmmaker Shane O’Sullivan reports that evidence doesn’t necessarily prove that Sirhan Sirhan shot and killed Kennedy by himself. New audio evidence seems to reveal at least 10 to 13 shots fired in the Ambassador Hotel’s kitchen that night; Sirhan’s gun held eight. Also, video and photographs show three senior CIA operatives and four unidentified associates at the hotel in the moments before and after the shooting. The CIA is one of the organizations implicated in the conspiracy theories. “There is strong evidence that Sirhan Sirhan was in a hypnotic state at the time of the shooting as a decoy for the real assassination,” O’Sullivan declares, “and that a second gunman fired the shot that killed Robert Kennedy.”

“Roman Polanski: Wanted and Desired” (9 p.m., HBO): For those who remember the scandal of Roman Polanski, and those who don’t, a fascinating documentary reopens this notorious case 30 years after it commanded world attention — and bred lasting misconceptions. “Roman Polanski: Wanted and Desired” is the saga of one of the world’s most famous directors (“Rosemary’s Baby” and “Chinatown”), who in 1977 was convicted for unlawful sexual intercourse with a minor. He pled guilty and served 42 days in jail. But trapped in a judiciary maze as well as a media circus, he had reason to believe he would never find justice. He fled from the United States to France, where he remains, still a celebrated filmmaker at 74. The documentary, by Marina Zenovich, profiles the Polish-born Polanski, whose mother was killed by the Nazis and whose marriage to actress Sharon Tate ended with her murder by followers of Charles Manson in 1969, when she was eight months pregnant. The film includes an interview with the victim, Samantha (Gailey) Geimer, now 45, who, as a 13-year-old, had been posing for Polanski during a photo shoot. And it explores the miscarriage of justice that has left Polanski a lifelong victim, too.

“Nashville Star” (9:30 p.m., NBC): After five years on cable, “Nashville Star” moves to the bigger stage of broadcast TV. Other changes include the addition of duos and groups to the singing competition and Mr. Hannah Montana — Billy Ray Cyrus — as host.