MOSCOW — A lawyer representing the family of Sergei L. Magnitsky, a Russian auditor and lawyer who died in prison in 2009 after uncovering a $230 million fraud targeting an American-born financier, suffered severe head injuries on Tuesday after plunging from his Moscow apartment building.

Russian news organizations said the lawyer, Nikolai Gorokhov, fell while helping movers carry a hot tub up to his fourth-floor apartment. They showed photographs of a shattered tub outside the building.

The financier, William F. Browder, said Mr. Gorokhov was to appear in a Moscow court on Wednesday to appeal on behalf of Mr. Magnitsky’s mother for an investigation into new evidence relating to the fraud scheme first exposed by Mr. Magnitsky.

“Basically, there is a trail of dead and seriously injured people leading from the Magnitsky case,” Mr. Browder said in a telephone interview early Wednesday. He said Russia’s post-Soviet version of the K.G.B., the Federal Security Service, or F.S.B., “is doing everything it can to shut down any serious investigation.”