A portrait of lawyer Sergei Magnitsky is held by his mother, Nataliya Magnitskaya, in Moscow in 2009. (Alexander Zemlianichenko/AP)

Natalia Veselnitskaya, the Russian lawyer who attended the June 9, 2016, meeting at Trump Tower with Donald Trump Jr., has for years been working to overturn the Magnitsky Act, a 2012 U.S. law that barred Russian officials suspected of human rights abuses.

Russian American Rinat Akhmetshin confirmed to The Washington Post on Friday that he also attended that meeting. He, too, has lobbied against the Magnitsky Act.

So what is the Magnitsky Act, and why is it the focus of so many powerful Russian interests?

The origin

The law is named after Sergei Magnitsky, a Russian lawyer and auditor who in 2008 untangled a dense web of tax fraud and graft involving 23 companies and a total of $230 million linked to the Kremlin and individuals close to the government. Magnitsky was the target of investigations, arrested by authorities and kept in jail without charges. He was beaten and later died under mysterious circumstances in jail just days before his possible release.

Independent investigators found “inhuman detention conditions, the isolation from his family, the lack of regular access to his lawyers and the intentional refusal to provide adequate medical assistance resulted in the deliberate infliction of severe pain and suffering, and ultimately his death.”

The law

The Magnitsky Act was signed by President Barack Obama in December 2012 as a retaliation against the human rights abuses suffered by Magnitsky. The law at first blocked 18 Russian government officials and businessmen from entering the United States, froze any assets held by U.S. banks and banned their future use of U.S. banking systems. The act was expanded in 2016, and now sanctions apply to 44 suspected human rights abusers worldwide.

Its official title is a mouthful — the Russia and Moldova Jackson-Vanik Repeal and Sergei Magnitsky Rule of Law Accountability Act of 2012. In most news stories and accounts, the shorthand is simply — the Magnitsky Act.

Bill Browder, an American hedge fund manager who hired Magnitsky for the corruption investigation that eventually led to his death, was a central figure in the bill's passage.

How does adoption factor in?

When pressed on the details of his meeting with a Kremlin-connected lawyer at Trump Tower in June 2016, Donald Trump Jr. appeared to downplay its significance by linking it to concerns over an issue that appears uncontroversial on its surface: adoption. But the barring of U.S. adoptions of Russian children is a flash point of tense diplomatic relations and tied directly to the Magnitsky Act.

Two weeks after Obama signed the Magnitsky Act, Russian President Vladimir Putin signed a bill that blocked adoption of Russian children by parents in the United States. Russia then also imposed sanctions on Browder and found Magnitsky posthumously guilty of crimes.

Supporters of the bill at the time cited mistreatment of Russian children by adoptive U.S. parents as the reason for its passage. But it was widely viewed as a retaliatory act, and the issues have been linked since.

Trump Jr. said that despite assurances that Veselnitskaya would come bearing incriminating information about Hillary Clinton in their 2016 meeting, the topic quickly shifted to the Magnitsky Act and U.S. adoptions from Russia.

Browder described Veselnitskaya in an NPR interview as a longtime foil to him in her efforts to repeal the Magnitsky Act. She represents a member of the Katsyv family, whose company is under investigation by the Justice Department in connection with the laundering of real estate money in New York. Denis Katsyv has lobbied to overturn Magnitsky and to end Russia's American adoption ban.