KAZAN, Russia -- Russian investigators are looking for clues to what caused the crash of a Tatarstan Airlines plane in Kazan that killed all 50 people onboard.
The investigators have found the plane's two black boxes. They have also started looking through the company's records Monday as part of the probe.
CCTV video footage from the airport shows the plane plunging into the tarmac vertically and then bursting into flames.
Russian Transport Minister Maksim Sokolov indicated that investigators were looking at crew error or technical failure among the possible causes of the crash.
"A mistake in the balance, the plane's technical fault, and poor quality fuel -- these are three versions [of what could have happened]," he said. "[Also] the ground crew's work and the weather conditions."
The Boeing 737 airliner crashed on a flight from Moscow late on November 17.
WATCH: CCTV Footage Of The Kazan Plane Crash
Irek Minnikhanov, a son of Tatarstan's President Rustam Minnikhanov, and the head of the local branch of Russia's Federal Security Service were among the passengers.
Officials said it would take weeks to identify the remains of some of the victims.
"There is a very large number of body fragments, and these fragments are located in a widespread area away the plane crash epicenter," said Tatarstan's Prime Minister Ildar Khalikov. "Therefore, the task for today is to get DNA information from the victims' relatives as quickly as possible."
Flags flew at half-staff in Tatarstan on November 18, and people were laying flowers at the airport.
Some voiced anger at the poor safety record of Russian airlines.
"It's unimaginable, it's awful, just awful," a man who gave his name as Dmitry, told reporters. "I would like to again remind our so-called controlling agencies not to give certificates to airplanes that everyone knows shouldn't be flying. Everyone already knows what state our national aviation is in. So, on the one hand this isn't surprising. It's just a shame that people die."
The plane that crashed was built 23 years ago and had seen service with seven other carriers before it was commissioned by Tatarstan Airlines. The plane had been in service with the company since 2008.
A year ago, the same aircraft was forced to return to the airport in Kazan while en route to Moscow due to a partial depressurization. There were no casualties in that incident.
In 2001, the same plane was damaged while landing in Brazil. At the time of that incident, it had 102 passengers and six crew members onboard but no one was injured.
Russian President Vladimir Putin has ordered the government to set up a commission for an urgent investigation of the Kazan accident.
Putin's spokesman, Dmitri Peskov, said the Russian president "expressed heartfelt condolences to the families and friends of those who died in the horrendous air accident."
With reporting by AP