Islamic extremists are suspected of carrying out the two bomb attacks this week, and an earlier one in October. Russia's top Islamic leader Doku Umarov is believed to be behind the suicide bomb attacks.
"That confirms the investigators' version that both terrorist attacks were linked," he told Russian television. "They could have been prepared in one place."
The remains of the presumed suicide bombers, including a "male finger with a pin from a grenade" found at the scene of the first bombing, were collected by Russian authorities for analysis.
Police Sergeant Dmitry Makavkin, 29, died in the first attack. He, and other police officers, were moving towards a suspicious looking woman when the bomb was detonated. This led investigators to initially claim the suicide bomber was a woman and even name her. However, footage from the scene and the discovery of the male finger caused confusion. Were the couple working together?
Security has been stepped up in Russia and was evident during New Year celebrations in Moscow as guards searched bags of those attending the traditional end of year firework display.
The Moscow Times reports a five-day period of mourning period began on Monday and will continue through Jan. 3.
In October a bomb attack in Russia raised fears that militant attacks would spread from the Muslim-dominated republics of the North Caucasus into other parts of Russia. This weeks two bomb attacks indicate that is happening.