A Russian lawyer jailed after uncovering evidence of police involvement in the theft of $230 million from the government has died in prison, officials said Tuesday, and his American partner is accusing the authorities of killing him.

Sergei Magnitsky, 37, a specialist in tax law and father of two, died at Moscow's Butyrskaya Prison of apparent heart failure Monday night, said Irina Dudukina, an Interior Ministry spokeswoman.