Russian investigators have found the two black boxes of a Boeing 737 jetliner, that crashed near the eastern city of Kazan on Sunday, killing all 50 people on board. The black boxes are crucial to determining the cause of the disaster. Alongside the investigations, work is also progressing to identify the victims.

"Both black boxes have been found. They were found on the crash site and now efforts are under way to retrieve them and hand them over to representatives of the Aviation Committee for further work," said Vladimir Stepanov, Russia's deputy minister for emergency situation.

"We are doing our best to complete the formalities as fast as possible. Formally, it is necessary to wait for documents confirming death, so our task is to make it possible for families and relatives to receive compensation before they receive all the required paper work," said Alexei Vovchenko, the deputy minister for labor security.

Russian Transport Minister Maxim Sokolov told reporters in Kazan that the plane was vertical when it hit the ground. But he added that the video recordings of the crash moment released on Monday were not of a very high quality because it was dark at that time.

He also said all the work parameters such as the engines and the plane itself will be studied by the inter-governmental aviation committee. He said that explanations for the crash could include a mistake in the balance, a technical fault, and poor quality fuel.

Sokolov noted "the ground crew’s work and the weather conditions" were other possible explanations.