Is it true that Marlon Brando's son, Christian, murdered somebody?

Yes. An excerpt:

Battling psychiatric problems, recovering from the severe auto accident that ended her modeling career and now pregnant by a man she felt was drifting away from her (Dag Drollet), Cheyenne Brando left Tahiti to stay at her father's Mulholland Drive compound high above the glamour of Hollywood.

Marlon knew his daughter was suffering from mental illness and he wanted her near him. He also reportedly distrusted the medical facilities on the island. "Marlon Brando has no confidence in French doctors, no confidence in the clinics in Tahiti," said Drollet's stepfather, Albert Lecaill, during court proceedings following his stepson's death. "He wanted her here for psychiatric care and to have her baby. Dag always wanted Cheyenne to go to Los Angeles to have her baby."

The invitation from her father in all likelihood could not have helped Cheyenne's fragile state of mind. She endured a love-hate relationship with Brando, alternately pleading for the actor to fulfill his role as father and pushing him away in an effort to create her own identity, separate from the great Marlon Brando.

Cheyenne and Dag were living apart when she accepted her father's offer to stay at his sprawling, 12-room home in Hollywood Hills atop the Santa Monica Mountains. After the accident she became reckless and much more aggressive than ever before, something her sister, Petra Brando, an attorney and filmmaker said was due to schizophrenia.
Despite their estrangement, Drollet accompanied Cheyenne to California and stayed with her in Brando’s two-acre, three-building iron-fenced compound. It was his hope that being in her father's company would help Cheyenne psychologically. It was the last chance for the relationship, Drollet told his family. If being with her father did not help her emotional state, Drollet planned to leave her once and for all. Cheyenne began psychological counseling, but Drollet told his father she was becoming increasingly unstable. Cheyenne was "very violent in her words and her manner. She has said very serious things, she has hit people . . . she hit Dag, when she was in a rage," Jacques Drollet told the Los Angeles Times.

Dag's father said later that Cheyenne reacted to Dag's ultimatums like a spoiled child used to getting her own way, setting the stage for tragedy.
Marlon Brando was well aware of his daughter's self-destructive behavior and took great pains to protect her from herself while she was living on Mulholland Drive. He locked up the kitchen knives and other sharp implements lest Cheyenne hurt herself. What he could not do was guard against the dangerous weapon that was his unbalanced and violent son, Christian.

With Christian, Dag and Cheyenne all in Southern California, the elements were in place for the tragedy to come. Dag and Cheyenne had been on the mainland a little over a week, and Dag had set up camp in the bungalow’s den. He and Cheyenne were not sleeping together.

On the final night of his life, Dag Drollet spent a relaxing evening alone in the den of Marlon’s home. Marlon acted as a typical Tahitian host, his relationship with Dag was good, and Marlon believed Drollet was a good influence on his troubled daughter. But Marlon preferred to be left alone.

Christian and Cheyenne went out for dinner that night at the elite Musso & Frank Grill where they had a long discussion about Drollet's violence. Unbeknownst to Christian, the abuse was a figment of her imagination.

Angry with the man who dared break up with her, Cheyenne weaved a tale of domestic assault and mental cruelty. Christian believed her. Cheyenne did not know what her brother would do upon returning home that night, and there are no signs that she intended for Christian to kill her lover. Most likely she was looking for sympathy and support.

“She went off on this bizarre tangent,” Christian told the Los Angeles Times later. “She kinda like got me going. I didn't stop to think.”

Dag was sitting in his bathrobe and shorts watching television when they returned. It was nearly 11 p.m., and Christian was drunk when he burst into the den to confront his sister’s lover. Christian had downed a six-pack of malt liquor and was drinking harder stuff when Cheyenne confessed that her lover was beating her and acting abusive.

Dag Drollet was more than six-and-a-half feet tall and had the well apportioned physique of a fit outdoor laborer. For this reason, the smaller Brando was carrying his .45-caliber revolver for protection when he went to tell off Drollet. The two men had met just hours earlier for the first time, so Christian had no idea what to expect.

"I did not go into that room to kill Dag Drollet," said Christian. "I just wanted to scare him.”

Drollet was sitting with his back to Christian and was preparing to roll a cigarette. He held the tobacco pouch in one hand and rolling papers in the other.

"Are you slapping around my sister?" Christian shouted as he burst into the room. "Lookit, don't do that anymore!" he yelled, moving in front of Dag, who was sitting down about to roll a cigarette. He pointed the revolver at Dag’s head. Whether Dag said something in return was never known.

Christian later told the court that he was moving to leave the room and still had his arm outstretched when the gun went off and the single slug hit Dag in the head. The entire exchange took a matter of seconds and when it was over, there was nothing Christian could do to save Dag.
"I just sat there and watched the life go out of this guy," he said later.

He was then arrested and tried for murder. Christian's fate after a long and arduous trial, was up to the judge. Prosecutors wanted the full 16-year term for Christian, while the defense, of course, wanted as little time as possible. Judge Robert Thomas split the difference and gave Christian a 10-year sentence. Under the sentencing laws then in place, given time off for good behavior plus the time he had already served, Christian could have been released to a halfway house in as soon as four years.

Christian was taken away to the California Men's Colony at San Luis Obispo to serve his sentence. The case faded from view and the Drollet and Brando families were left to pick up the pieces. The Drollet clan left the United States believing that they had been done an injustice and that Christian had gotten away with murder. Marlon Brando's oldest son had been taken away from him and his daughter was all but emotionally destroyed.

Cheyenne continued her downward spiral, now formally diagnosed with schizophrenia, a particularly cruel mental illness that convinces its victims that they have no illness at all. Over the next several years she was on and off her medication many times.

"As she slowly withdrew, I struggled to maintain the bond we had always shared," Petra Brando wrote later. "A feeling of alienation set in when I began to understand that the dark journey through mental illness is an individual one that I could not enter or share and that she must travel alone."

She suffered abandonment from Tahitian friends who could not help but gossip. She expressed several times that when she thought of Dag, she wished to join him in death.

A month short of the five-year anniversary of the shooting, the case was brought back to the front pages. Cheyenne Brando, who had just lost custody of the son she conceived with Dag Drollet, hanged herself in her mother's home. She was just 25 years old.

Christian was still incarcerated at the time. He has since been released and is living a quiet life far from the spotlight, content just to be Christian Brando, a welder. He was involved, briefly, in the Bonnie Lee Bakely murder case when there was some doubt as to whether Robert Blake or Christian fathered Bonnie’s child. Tests showed Christian was not the father. It is likely that he will be called as a witness, because he was heard on tape warning Bonnie that her lifestyle could get her killed. Christian is not a suspect in that case.

Perhaps in shared pain there can be healing. At Marlon Brando's request, his former friend Jacques Drollet, now his sworn enemy, agreed that Cheyenne would be buried in the Drollet family crypt next to her slain lover.

In the major newspaper in French Polynesia the headline after the funeral read "Cheyenne and Dag: Together For Eternity."

From:
http://www.crimelibrary.com/notorious_murders/family/christian_brando