I came across the Magnitsky act, according to which:
The Magnitsky Act, formally known as the Russia and Moldova Jackson–Vanik Repeal and Sergei Magnitsky Rule of Law Accountability Act of 2012, is a bipartisan bill passed by the U.S. Congress and signed by President Obama in November–December 2012, intending to punish Russian officials responsible for the death of Russian tax accountant Sergei Magnitsky in a Moscow prison in 2009. Since 2016 the bill is applied on a global scale by the US government.
Why is US government taking any steps to punish the Russian officials involved in the death of Sergei Magnitsky (who is a Russian accountant)?