MOSCOW (AP) -- A liberal Russian economist who has criticized President Vladimir Putin's policies said Friday he fled Russia on a day's notice because of fears of losing his freedom on "very bogus grounds."

Sergei Guriev told The Associated Press that he wanted to escape pressure from a new criminal investigation around jailed oligarch Mikhail Khodorkovsky, once Russia's richest man.

In a 25-minute phone conversation from Paris, where he arrived on a one-way flight on April 30, Guriev said he feared he could share the fate of witnesses in two previous investigations into Khodorkovsky who were later charged and died in prison.

"I don't see under what circumstances I can return," he said.

Investigators began proceedings early this year against the authors of an expert report commissioned by then-president Dmitry Medvedev in 2011, to which Guriev contributed, that criticized Khodorkovsky's conviction in late 2010 for embezzling oil. He had been imprisoned since 2003 on charges of avoiding taxes on the same oil.

Khodorkovsky is due to be released early next year, and Russia's supreme court is to reconsider the verdict in the second case in August. His supporters fear, however, that investigators are preparing a third set of charges to ensure he remains in jail.

According to investigators, the authors of the report had a conflict of interest because they had previously received money from Khodorkovsky.

Guriev denied receiving money from Khodorkovsky's oil company, Yukos, once Russia's largest, or bank, Menatep. However, Guriev said that he did not consider that it would have been illegal to do so.

Two of the other five experts have been questioned by investigators but have not been charged.

Guriev began to worry when investigators interrogated him three times and searched his office, seizing hundreds of pages of documents and 45 gigabytes of emails dating back five years, on grounds he described as "extremely absurd."

Though Guriev is only a witness in the case, he said his shock at investigators' "lack of respect for the letter and spirit of the law" made him worry that they could name him as a suspect and take his passport away.

Guriev said he could not discuss the interrogations because he had signed a non-disclosure agreement. However, he said investigators informally told him that he was fair game for legal pressure because he had "started his political activity" in 2008, when he began advising Medvedev.

Guriev's family moved to Paris without him 3 and a half years earlier. "If it were part of a bigger plan, I would have of course moved before," he said.

Guriev said he regretted not listening to his wife, economist Ekaterina Zhuravskaya, who left with their children for France after a spousal dispute over Russia's future. Zhuravskaya "turned out to be a wiser and more sane person than I was: I was less cynical, she was more," he said.

"She's an academic, I'm an academic: we talk in terms of general probabilities, scenarios, various options, and one of those options materialized. There are some people who get in trouble for this and some people who get in trouble for that, and I got in trouble for this," he added.

Guriev, who ran Moscow's respected New Economic School from 2005 until his departure, has long enjoyed the reputation as one of Russia's top economists and something of a maverick. U.S. President Barack Obama spoke at the school while on a state visit in 2009 which both sides used as a springboard for improving relations.

When Medvedev was president from 2008 to 2012, Guriev was an informal government advisor and was seen as a key figure encouraging Westerners to invest in Russia.

Guriev's sudden departure has made him a poster boy for the uncertainty and fear gripping liberal members of the Russian elite. On Friday, Guriev polled the maximum possible among all candidates to the board of state-run banking giant Sberbank, even beating its chairman German Gref, though Guriev had withdrawn from the running after leaving Russia.

Liberal figures who flourished under Medvedev, who is now prime minister and widely derided as weak, have come under heavy fire since Putin returned to the presidency last year.

Leading Kremlin strategist Vladislav Surkov, who is believed to have pushed for Medvedev to remain president, resigned earlier this month after a public spat with investigators over attempts to develop a Russian Silicon Valley, one of Medvedev's flagship projects.

Akhmed Bilalov, whose cousin went to university with deputy prime minister Arkady Dvorkovich, one of Medvedev's top advisors, was fired from Russia's Olympic Committee after a public upbraiding from Putin and left Russia claiming that his office had been poisoned with mercury. Dvorkovich has been engaged in a semi-public dispute for months with Rosneft CEO Igor Sechin, a close Putin confidante thought to head the Kremlin's hawkish faction.

"In the last year we've seen a lot of things which we thought are impossible," Guriev, said. "Some people who were high profile are now no longer there."

After the wave of pressure from investigators began, Guriev reached out to high-profile connections in Russia's government. In April, a senior official told him that he was in the room when Putin called chief investigator Alexander Bastrykin and told him that there was no reason to investigate Guriev.

In May, after he left, senior figures told Guriev that he had nothing to worry about and could return to Russia, but that Putin had said he could not interfere with investigators' work.

Putin's spokesman Dmitry Peskov told Russian media earlier this week that Guriev's departure was a personal matter and that the Kremlin had no hand in it.

Despite his closeness to the Kremlin, Guriev was equally ready to associate himself with Kremlin critics. He publicly contributed to opposition leader Alexey Navalny's anti-corruption foundation and criticized an ongoing prosecution of Navalny for alleged timber embezzlement as without merit.

While being used to promote Russia at major investment forums, Guriev rarely shied from criticizing Russia's oil-and-gas-driven economic model. Speaking alongside Medvedev as the latter offered optimistic visions of Russia's future, Guriev frequently warned that a sharp drop in the oil price would eviscerate the Russian economic system. Guriev supported privatization of state-run companies, a move strongly opposed by figures like Sechin.

The most troubling sign for Guriev came when he and his wife noticed that authorities put red flags on their passports after the Khodorkovsky investigation began. "When the border officer entered my passport, he lost speech and called his superiors," who told him to enter additional information and copy all the pages of the passport, Guriev said.

When Guriev asked investigators why this happened, he said officials told him that monitoring his travel was part of the investigation.

"They never hid their political agenda," Guriev said. "A lot of people in Russia think that the actions in my case are normal and I should have stayed," he added. "But I think I had no choice."

Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.