Complex sentence: An independent public commission to investigate the bombings, which was chaired by Duma deputy Sergei Kovalyov, was rendered ineffective because of government refusal to respond to its inquiries.
Split into simpler sentences: An independent public commission to investigate the bombings was chaired by Duma deputy Sergei Kovalyov. However, the public commission was rendered ineffective because of government refusal to respond to its inquiries.