Bortnikov said Russian President Vladimir Putin had been informed of the detention.
Boris Nemtsov, an outspoken critic of President Vladimir Putin and Russia’s role in the Ukraine crisis, was shot dead steps from the Kremlin in a murder that underscored the risks taken by the Russian opposition.
Nemtsov, 55, was shot four times in the back by assailants in a white car as he walked across a bridge over the Moskva River in central Moscow with a Ukrainian woman, who was unhurt, just before midnight on February 28.
