The Magnitsky Act, which freezes the assets and bans visas for certain Russians, including those close to Vladimir Putin, "touched off a nasty confrontation with the Kremlin, and the two sides have been trying ever since to undermine the credibility of the other. Recently, however, Russian prosecutors have taken that effort to a remarkable new level, claiming that Mr. Magnitsky was actually murdered by Mr. Browder," according to The New York Times.

http://www.npr.org/sections/thetwo-way/2017/10/23/559463071/state-department-reportedly-revokes-visit-of-magnitsky-act-campaigner

Sergei Magnitsky, a Russian lawyer who died in prison in suspicious circumstances, was found guilty of tax evasion on Thursday in a posthumous trial that has further damaged President Vladimir Putin’s reputation in the West.

https://www.reuters.com/article/us-russia-magnitsky/russia-convicts-lawyer-magnitsky-in-posthumous-trial-idUSBRE96A09V20130711