In testimony before the Senate Judiciary Committee Thursday, financier Bill Browder is expected to uncover another shocking revelation about Fusion GPS, the left-wing firm responsible for both the Trump-Russia dossier and the misleading defense of Planned Parenthood after the Center for Medical Progress sting videos. According to Browder’s prepared remarks submitted to the committee ahead of his testimony, the firm spread vicious lies about Sergei Magnitsky, a Russian lawyer who was imprisoned and killed for exposing corruption in Putin’s regime.

Browder’s testimony will dwell on the Russian government’s attempts to repeal a law passed in retaliation for abuses against Magnitsky, the Magnitsky Act. Russian attempts to repeal the law reached a fever pitch last year in Washington, and Browder will allege that the actors involved in this effort did not disclose their roles as agents for foreign interests, thus violating the Foreign Agents Registration Act. One of the notorious players in this game was none other than Fusion GPS.

Before addressing Fusion GPS, Browder will detail Magnitsky’s story. The financier — founder and CEO of Hermitage Capital Management, one of the largest investment advisers in Russia — will explain that in 2000, when Russian President Vladimir Putin first took power, he had to rein in the oligarchs. At first, Browder and Putin had the same enemies, so exposing corruption helped Putin.

In 2003, that all changed, and by 2005, Putin was targeting Browder. The financier hired Russian lawyer Sergei Magnitsky to investigate raids against his offices. Magnitsky uncovered astounding examples of identity theft and government corruption. For these discoveries, the lawyer was captured by Russian authorities and imprisoned.

Magnitsky was treated horribly and kept an official record of abuses against him by filing official complaints. He died on November 16, 2009, leaving behind a wife and two children. “Sergei Magnitsky was murdered as my proxy. If Sergei had not been my lawyer, he would still be alive today,” Browder’s testimony declares. So he pledged to “seek justice and create consequences for the people who murdered him.”

Browder’s efforts led to the Sergei Magnitsky Rule of Law Accountability Act, which froze assets and banned visas for those who killed Magnitsky, as well as for other Russians involved in human rights abuses. The bill passed the House (364 to 43) and the Senate (92 to 4) in November 2012 and was signed by President Obama in December that year.

Putin retaliated in the worst way possible. He banned the adoption of Russian orphans by American families. This was particularly horrible, Browder will argue, because Russia did not allow the adoption of healthy kids, only sick ones. American families adopted children with HIV, Down syndrome, and other ailments.

But thanks to Putin, these sick children would not be adopted by Americans. Instead, they would stay in the Russian orphanage system, which did not have the resources to properly care for them. Most would die before their 18th birthday, Browder will argue. “In practical terms, this meant that Vladimir Putin sentenced his own, most vulnerable and sick Russian orphans to death in order to protect corrupt officials in his regime.”

The Magnitsky Act hit Putin hard, according to Browder’s testimony, because he keeps a great deal of his money in the West (where property rights are a thing) and because it struck at Putin’s ability to reward his cronies in similar ways.

So Putin launched a campaign against the Magnitsky Act. Here’s where Fusion GPS comes in.

Many Americans are familiar with a Russian lawyer named Natalia Veselnitskaya, who infamously met with Donald Trump Jr. and Paul Manafort, promising them dirt on Hillary Clinton which she never delivered. Instead, she pressed them on the Magnitsky Act and the adoption of Russian children.

But Veselnitskaya did not just reach out to the Trump campaign. She also hired Fusion GPS to undermine the story of Magnitsky.

Veselnitskaya, through Baker Hostetler, hired Glenn Simpson of the firm Fusion GPS to conduct a smear campaign against me and Sergei Magnitsky in advance of congressional hearings on the Global Magnitsky Act. He contacted a number of major newspapers and other publications to spread false information that Sergei Magnitsky was not murdered, was not a whistle-blower, and was instead a criminal. They also spread false information that my presentations to lawmakers around the world were untrue.

Yes, Glenn Simpson and Fusion GPS were paid by a Russian lawyer to slander Browder and Magnitsky, pushing Putin’s goal of repealing the Magnitsky Act.

This heinous job fits with Fusion GPS’s most notorious projects: the Trump-Russia dossier and the Planned Parenthood “forensic report.”

The firm, founded in 2010 by former Wall Street Journal reporter Glenn Simpson, has a long history of attacking Republicans and conservatives — which has played into Russian interests.

In 2012, the firm aimed its guns on donors to Republican nominee Mitt Romney, an outspoken critic of Putin who warned that Russia was America’s biggest foe on the global stage. (Remember when Democrats, led by Barack Obama, dismissed these complaints as a 1980s holdover?) President Obama’s campaign website attacked a Romney donor by name, and Kimberley Strassel traced these attacks to none other than Fusion GPS.

Interestingly, a wealthy Republican donor strongly opposed to Trump hired Fusion GPS to create the Trump-Russia dossier, according to a New York Times exposé. He backed out of the project, and Democrats took over.

In 2015, when the Center for Medical Progress (CMP) released sting videos showing Planned Parenthood staffers agreeing to sell aborted babies for profit, Fusion GPS compiled a misleading report that suggested the videos were false.

The firm’s “forensic report” attempted to discredit the videos as manipulations, selectively edited clips that twisted Planned Parenthood staff out of context. Ironically, buried in the report was the concession that there was no “widespread evidence of substantive video manipulation.”

Even so, many media outlets bought the insinuations. Politico‘s story: “Report for Planned Parenthood finds sting videos manipulated.” The New York Times went with “Planned Parenthood Videos Were Altered, Analysis Finds.”

Now this left-wing firm has been decisively linked to Vladimir Putin’s interests — and the very Russian lawyer who reached out to Donald Trump Jr.

Fusion GPS twisted the truth to attack Romney donors, helping Russian interests. It twisted the truth to defend Planned Parenthood. But perhaps no project is as heinous as its aid to Putin by smearing the good name of a whistleblower who was brutally murdered by Putin’s regime.

Glenn Simpson has agreed to speak to the Senate Judiciary Committee behind closed doors, after previous reports saying he will plead the Fifth. He certainly has a great deal to hide.