The mother of a man who was found dead inside the apartment of Ed Buck, a political activist and Democratic donor in Los Angeles, has filed a wrongful-death lawsuit against him, as the authorities continue to investigate how two men were found dead in his West Hollywood apartment in less than two years.

In the lawsuit, filed in Los Angeles this week, the mother, LaTisha Nixon, said that Mr. Buck injected her son, Gemmel Moore, with a lethal dose of crystal methamphetamine in 2017. The Los Angeles County medical examiner’s office had ruled that Mr. Moore died from an accidental methamphetamine overdose.

Another man, Timothy Dean, was found dead in Mr. Buck’s apartment last month. A cause of death has not been released in that case.

Both Mr. Moore and Mr. Dean were black, which raised suspicions among political activists and critics of Mr. Buck, a white man in his 60s who has given more than $116,000 to Democratic candidates and groups in the past decade or so. Protesters gathered this year outside Mr. Buck’s apartment to demand justice after the second death, and the men’s families have accused Mr. Buck of preying on black gay men.