The Federal Bureau of Investigation interviewed suspected marathon bomber Tamerlan Tsarnaev in 2011 at the request of the Russian government, but didn't find evidence of suspicious activity and closed the case, an FBI official said Friday.

The fact that the FBI spoke with Mr. Tsarnaev, who was killed Friday morning in a firefight with authorities, is likely to become a focal point of the post mortem into how the attack was able to be carried out at the Boston Marathon. It also speaks to the challenge faced by authorities as...