|Khodorkovsky, who onced the Yukos oil company, is set to stay in prison until 2016 [Igor Kharitonov/EPA]
Russian outgoing president, Dmitry Medvedev, has ordered the prosecutor general to examine the legality of 32 criminal cases, including the jailing of Mikhail Khodorkovsky, the former oil tycoon.
Khodorkovsky, who once owned the Yukos oil company, was arrested in 2003 and jailed on tax evasion and fraud charges.
His detention came soon after he showed political ambitions to take on Vladimir Putin, who won Russia's presidential election on Sunday.
Khodorkovsky received a new sentence in 2010, and is set to stay in prison until 2016 in a case that opponents of Putin say is politically motivated.
Medevedev remains president until May, when Putin will be inaugurated. He has ordered the prosecutor to report back by April 1.
Khodorkovsky's lawyer, Vadim Klyuvgant, told the Reuters news agency the true significance of Medvedev's initiative could be judged only when the outcome of the investigation was known.
"There's been so many ... orders that you run out of words to comment," he said by telephone.
"But if ... the prosecutor and the president start to conform with the law, we will know it from the result. The lawlessness of this sentence is so glaring that there's nothing to study there."
Khodorkovsky's former business partner, Platon Lebedev, was also on the list of cases Medvedev ordered the prosecutor general to study and report back.
List of political prisoners
The order followed a meeting last month at which opposition leaders handed Medvedev a list of people they regard as political prisoners and want released from prison.
Putin has called Khodorkovsky a "thief" who should sit in jail. Medvedev said last year he saw no threat if Khodorkovsky were freed.
Last year Medvedev asked legal experts to look into Khodorkovsky's case along with other prominent cases, but the initiative resulted in no review of the court decision.
Prosecutors have said Khodorkovsky stole $27bn in oil from subsidiaries of Yukos through pricing schemes and laundered some of the money, charges his lawyers dismissed as an absurd, politically motivated pretext to keep him behind bars.
Khodorkovsky, one of the tycoons who made fortunes in the chaos following the collapse of the Soviet Union in 1991, denies any wrongdoing.
He says he has been prosecuted over business practises that were both legal and widely used.