her home was a safe place until it became the scene of her murder. shot four times in the entrance of her moscow apartment in 2006 and sal rander litvenyenko, former kgb officer died a slow death after drinking a legal dose of radioactive polonium. his tea spiked in a london hotel during with a meeting with two former russian servicemen all outspoken critics of president vladimir putin, all killed in mysterious ways. we still don t know who ordered those killings and now we have this one. what do you think those deaths have in common? well i don t think they have anything in common. reporter: the kremlin denied any involvement in the cases. former kremlin adviser believed president putin is innocent. there s absolutely no proof of any involvement of the russian state. reporter: those suspicious deaths are not the only ones.