WASHINGTON — Six years after his mysterious death in a Moscow prison cell, Sergei L. Magnitsky has become a byword for brutality in President Vladimir V. Putin’s Russia. Now, a documentary film that paints Mr. Magnitsky as an accomplice rather than a victim is generating a furor, with critics trying to block a screening of it next week in Washington.

Screenings of the film, “The Magnitsky Act — Behind the Scenes,” have been canceled in Europe after threats of libel suits from William F. Browder, an American-born financier who fell afoul of the Russian government and hired Mr. Magnitsky, a lawyer and auditor, to investigate a vast tax fraud scheme after the government seized three of his Russian subsidiaries.

“The Magnitsky Act” is to be screened on Monday at the Newseum, a private museum dedicated to the news industry. Lawyers for Mr. Browder and Mr. Magnitsky’s mother, Natalia Magnitskaya, sent a letter to the Newseum this week demanding that it call off the event. After a conference call on Thursday, the museum’s management refused.

“We stand for free speech and free expression,” said Scott Williams, the chief operating officer of the Newseum. “We’re not going to allow them not to show the film.” He noted that the museum was not sponsoring the screening, but merely renting out its theater. “We often have people renting for events that other people would love not to have happen,” he said.