Marilyn Monroe. John Lennon. Whitney Houston. Natalie Wood. Princess Diana. Many of our most famous celebrities have died leaving questions behind about what really happened during their last hours.

My new thriller SHOOTING FROM THE STARS is about the murder of a legendary movie star named Laura Marlowe. And I draw on some of the mysteries still surrounding the real-life deaths of John Lennon, Sharon Tate and others to tell the story in my novel.

Here are 10 famous celebrity deaths that we still don’t have all the answers for:

WHY WAS MARILYN MONROE’S DEATH NEVER INVESTIGATED AS A MURDER?

One of the first police officers to arrive at the scene of Marilyn Monroe’s death thought she had been murdered. Authorities weren’t called immediately after her body was found. And there was conflicting evidence about whether the drugs found in her back up the ruling she died of a pill overdose. So why wasn’t there ever a murder or real criminal investigation into her death? Probably because of the times back in 1962 – the power of the Hollywood studios, her connections with the Kennedys and the trust in the press to tell a story without too many questions being asked. Imagine how a story like Marilyn Monroe’s death would be covered today by TMZ, the 24-hour news networks and social media. Not too many people believe Marilyn was actually murdered. It’s more likely her death was accidental. Or maybe it was a suicide. But it sure would have been nice to hear all of the facts instead of leaving us with these questions more than a half century later about how America’s favorite sex symbol really died.

HOW DID MARK DAVID CHAPMAN PICK JOHN LENNON TO SHOOT?

The sad truth is Chapman himself doesn’t even seem to know the answer. He’s talked about being influenced by J.D. Salinger’s novel “The Catcher in the Rye”; being upset that Lennon called the Beatles more popular than Jesus (even though Lennon had said this some 15 years earlier); and being angry about Lennon’s affluent lifestyle in New York City. He also claims he had a list of other targets in mind, including Johnny Carson, Marlon Brando, Walter Cronkite, Elizabeth Tayor, George C. Scott and Jacqueline Kennedy Onassis. Chapman is serving a sentence of 20 years to life and is unlikely to ever be released from prison.

HOW COULD WHITNEY HOUSTON DROWN IN A FOOT OF WATER?

Pop icon Whitney Houston “drowned” in a bathtub – filled with only a foot of water. How did that happen? Doctors determined Houston didn’t suffer a drug overdose, even though she had cocaine and some other drugs in her body. She didn’t have a heart attack, the other likely scenario – even though she had some heart issues. The singer was found face down in a foot of very hot water. The best speculation is that she had a seizure – brought on by some combination of the drugs and her heart condition – that left her unconscious. Tragically, of course, Whitney Houston’s daughter, Bobbi Kristina, was found unconscious in a bathtub earlier this year with many of the same unanswered questions. Bobbi Kristina remains in a coma and on life support.

DID ANYONE HEAR NATALIE WOOD’S SCREAMS FOR HELP?

Actress Natalie Wood drowned on the night of November 29, 1981 while on a boat off Santa Catalina Island with husband Robert Wagner and actor Christopher Walken. The most-told account is that Wood – after drinking and an argument involving her, Wagner and Walken – – went up on deck, then accidently slipped and fell overboard. No one saw her go into the water, but did anyone hear her cries for help? Wagner says they assumed at first she went to bed and didn’t realize until later she was missing. The captain of the boat says he never heard any screams on the bridge. But a witness from another boat recently came forward to say she heard a woman screaming for help in the water for nearly 15 minutes that night – and tried in vain to get help. Natalie Wood’s death remains one of the great celebrity mysteries of all time.

DID THE PAPARAZZI KILL PRINCESS DIANA?

After Princess Diana died in a tragic Paris car crash in 1997, everyone immediately blamed the celebrity photographers that were following her – and who she was trying to elude in the speeding car. “The paparazzi killed Diana” became a popular refrain. People railed against the celebrity press at Diana’s funeral. Tabloid newsstand sales plunged. But authorities later cleared the photographers of any wrongdoing. Most of the blame was ultimately put on the driver of Diana’s car. And all sorts of other conspiracy theories have popped up since with other scenarios of how Diana might have actually been murdered. No one will probably ever know for sure what happened that night, but we now know the answer is a lot more complicated than just blaming the paparazzi.

DID CHARLES MANSON KILL SHARON TATE BY MISTAKE?

The question of why the Manson family brutally murdered actress Sharon Tate and her unborn child in the summer of 1969 has never been completely answered. Was Tate the intended target or was she just in the wrong place at the wrong time? There has long been speculation that Manson was really out to get record producer Terry Melcher – who Manson blamed for rejecting his music. Melcher, the son of Doris Day, had lived in the house before Tate and her husband director Roman Polanski, and it was assumed by many Manson didn’t know Melcher had moved. But other accounts say Manson was aware Melcher was no longer there and simply wanted to kill whoever was now in that house to send some sort of gruesome message to the Hollywood establishment.

WHO MURDERED COLONEL HOGAN?

Bob Crane became a big TV star on “Hogan’s Heroes” – an unlikely hit sitcom in the 60s about the wacky hijinks in a German P.O.W. camp. But behind his loveable, wise-cracking Col.Hogan character, Crane had a dark secret sex life and frequently took pictures of his X-rated activities. He was found bludgeoned to death – with an electrical cord wrapped around his neck – at his Scottsdale, Arizona apartment on June 29, 1978. Authorities found hundreds of pornographic photos and home movies showing him having sex with different women. A friend named John Carpenter was later tried for the murder, but acquitted. No one knows if Crane’s sex addiction led to his death. But, more than 35 years later, his murder remains unsolved.

WHY DID TV FUNNYMAN PHIL HARTMAN’S WIFE MURDER HIM IN HIS SLEEP?

TV comic Phil Hartman – who soared to fame first on Saturday Night Live and later on the sitcom “NewsRadio” – was shot to death by his wife Brynn at 3 a.m. in the morning as he slept in their bed. The Hartmans’ two young children were in the house at the time of the murder, and no one could ever understand why she did such an unthinkable thing. One theory is that Brynn – who had been in and out of rehab – was out of control due to a volatile mix of alcohol and drugs. Another was that she was jealous of her husband’s success, while her own show business career had floundered. And friends said the couple – who acted happy in public – argued constantly when they were alone. Brynn Hartman later that night turned the gun on herself and committed suicide, taking the answers about why she did it to the grave with her and her husband.

WAS SUPERMAN RUBBED OUT BY THE MOB?

The official story is that TV Superman George Reeves committed suicide by shooting himself in the head on June 16, 1959 because he was depressed over being typecast as a cartoon character actor. But there has been speculation he was murdered – possibly by a mob hitman. The theory was Reeves’ womanizing – he’d recently broken off an affair with a married woman and had a volatile relationship with another woman – had gotten someone mad enough to put out an underworld contract on his life. People close to Reeves always doubted the suicide verdict and said he had never been happier. But the more likely explanation is his death was simply a tragic accident: Reeves was drunk with a .27 blood alcohol level content when he died.

DID ANDY KAUFMAN FAKE HIS OWN DEATH?

Like with Elvis and Jim Morrison, there are people who believe comic Andy Kaufman faked his death to escape the public spotlight. Or maybe just to pull the ultimate practical joke on his fans. Kaufman, of course, was known for doing bizarre and unorthodox stunts during his career. He also had told many people he wanted to fake his own death – and almost seemed obsessed by the idea. Some of those close to Kaufman have claimed they know for a fact that his death was just a prank which he planned to reveal at some point. And the Jim Carrey movie “Man on the Moon” about Kaufman leaves open the question of whether he is dead or alive. Kaufman had reportedly said that if he did ever fake his death, he would come back 20 years later to tell the world it was all a joke. It’s now been more than 30 years since he died of cancer in 1984, so it seems like the joke is over. But there are diehard fans still waiting for Andy Kaufman’s return.

R.G. Belsky is a New York City journalist and author. He was the news editor for Star magazine; managing editor of the New York Daily News; metropolitan editor of the New York Post; and a managing editor at NBC News. SHOOTING FOR THE STARS (Atria – August 11) is the second book in the Gil Malloy series – following up on last year’s highly-acclaimed thriller THE KENNEDY CONNECTION.