Real estate heir and alleged serial killer Robert Durst denied that he killed his close friend, Susan Berman. Durst reiterated his innocence in the murder when he testified at his trial Monday.

During his stand at his murder trial, Durst also denied that he knew who had killed his friend and one-time media representative during his wife's disappearance. The 78-year-old heir to a billion-dollar real estate empire is accused of killing Berman, who was found shot in the head in her home in Los Angeles in 2000.

Durst appeared in court in a wheelchair and seemed like he was in bad health. Durst, a member of one of New York's wealthiest families, spent most of his testimony talking about his ailments and early life story, including his long-time friendship with Berman.

Prosecutors alleged that Durst killed Berman because she knew too much about the 1982 disappearance of Durst's wife, Kathleen McCormack Durst. While Durst was never charged over his wife's disappearance, prosecutors believe he may have killed her after she threatened to divorce him.

In 2001, Durst was arrested for murder and dismembering of his former landlord and neighbor, Morris Black. Durst had rented an apartment from Black while he was in hiding during the reopening of investigations into his wife's disappearance. Durst was eventually acquitted in 2005 after his lawyers claimed that he only acted in self-defense.

Durst's life became the focus of a hit HBO documentary series titled "The Jinx: The Life and Deaths of Robert Durst." During a taping of one of the last episodes, Durst appeared to have confessed to the murders when he forgot his microphone was still on.

After he was acquitted of Black's murder, authorities continued to build a case against him over Berman's murder and his wife's disappearance. Durst was arrested in May 2015 during the premiere of the documentary's final episode.

The deaths of the people close to Durst have attracted intense media scrutiny. Prosecutors believed Durst might have killed Kathleen and then assassinated Berman because she knew about the murder and prepared to talk to authorities. The whereabouts of his wife and questions of what had happened to her remain unanswered.