A Swiss cop is under investigation for meeting with a Russian lawyer at the center of the infamous Trump Tower meeting.

The cop, a money-laundering investigator, had a brief meeting with Natalia Veselnitskaya in Moscow in December 2016, sources told Fox News. That unauthorized and questionable meeting is now being probed by Swiss prosecutors, who are trying to determine whether she was trying to "turn" Swiss law enforcement or attempting to recover a client's account that was frozen in Switzerland.

Although small in size, Switzerland controls approximately $2.5 trillion dollars in global offshore assets -- a whopping 25 percent of such monies and assets and proudly claims secrecy and discretion for anyone who chooses to bank there.

Suspects in criminal cases are also afforded privacy in Switzerland and Fox New is calling the investigator “Mr. K.” The Swiss Prosecutor’s Office will only say that he is the subject of a criminal investigation. But sources tell Fox News he is being investigated for “corruption, abuse of power, and violating professional secrets.”

He was fired from his office after traveling to Moscow in late December of 2016, against the will of his boss, and largely on the dime of the Russians.

“Mr.K.” is a federal police officer—one of the few in the department who speaks Russian. He has been at the center of the important Swiss cases involving Russian money laundering. Veselnitskaya has been at the epicenter of political intrigue in the United States.

Investigative journalist Thomas Knellwolf has been covering the case closely for the Swiss paper Tages-Anzeiger.

“The big questions in the Swiss criminal investigation are: What did he talk about when he was on his private trip to Moscow and also in his unofficial meetings with the Russians,” Knellwolf told Fox News in an email. “Did he reveal secrets? Did he get more than two nights in a first class hotel paid for by the Russian state?”

In an email to Fox News, Veselnitskaya believes this is a conspiracy about “Mr. K.” and Russia.

“If he is the very policeman who was dismissed (his name is redacted from the judgement of the Swiss administrative court, as are the names and details of all other persons), then it is obvious to me that he was removed for honestly doing his work,” she wrote.

Mr. K. was, reportedly, lured to Moscow by the deputy prosecutor general of Russia with the promise of a look at some confidential documents. Those documents, in the end, weren’t made available. But Veselnitskaya, a high-power Russian lawyer, was— and she and Mr. K met during his mysterious two-day visit to Moscow, sources say.

Veselnitskaya is the same Russian lawyer who briefly met with Donald Trump Jr. and others including Paul Manafort and Jared Kushner six months earlier on June 9, 2016. They thought she had dirt on then presidential candidate Hillary Clinton. She claims she wanted to discuss Russian adoptions.

“What it shows is that Russia is not just disrupting the political and government process in the U.S., but they are also doing it in Switzerland. Both of these things trace back to the Magnitsky Act and it shows how much Putin hates it,” said Bill Browder.

The Sergei Magnitsky Rule of Law Accountability Act was passed into U.S. law in 2012. It sanctions and freezes the assets of those the U.S. Congress deems to be human rights abusers. Bill Browder was the man who pushed the bill through. He was a major investor in Russia shortly after the fall of the former Soviet Union.

Browder’s lawyer Sergei Magnitsky died at the age of 37 after being beaten in a Russian jail in 2009 —while investigating what happened to $230 million Browder claims he paid to the Russian government in tax, but that was stolen by corrupt officials in an elaborate scheme. The Magnitsky Act sanctions those who the U.S. Congress deems are in some way responsible for Magnitsky’s death and the fraud.

In retaliation, Russian President Vladimir Putin banned adoptions of Russian children by Americans who he insisted are human rights abusers, too, citing a few cases of adoptions that ended badly.

Veselnitskaya is pushing back hard against the Magnitsky Act and its biting sanctions, on behalf of her client Denis Katsyv and some would say also on behalf of the Kremlin. Both she and the Kremlin deny that they are in cahoots.

Denis Katsyv, whose father is a politically connected wealthy business man in Russia, has $8 million frozen in Switzerland by the Magnitsky Act. Browder believes Katsyv is one of the key people laundering his stolen funds. Katsyv owns Prevezon Holdings which has multiple real estate properties in New York City. Those assets were also frozen by the U.S. government. The case, which dragged on for years, was settled before the U.S. District Court of Appeals in Lower Manhattan in May 2017 for $6 million with the help of Veselnitskaya and a highly paid army of lawyers and advisers, including Fusion GPS’s Glenn Simpson. However, nearly a year later, no money has been paid, according to the latest court records reviewed by Fox News.

Simpson has also been part of the lobbying effort to overturn Magnitsky. And for a steep price. In released Congressional testimony, Simpson has said that Fusion GPS bills some clients $50,000 a month.

Meanwhile, Veselnitskaya is barely able to hide her contempt for Bill Browder. She said any meetings she had with the Swiss were official, from her point of view, and done “to defend my client against the slanderous allegations made by Mr. Browder.” She maintains he invented his tax fraud story and won’t admit Magnitsky was killed in prison. Incidentally, Browder was convicted in absentia in Russia for tax fraud.

In her email response, the Russian lawyer wrote: “Unfortunately, Switzerland made itself a tool in William Browder’s hands." And, Veselnitskaya added, “This is a coordinated defamation attack on me as a lawyer whose professional activities have recently become extremely dangerous for Mr. Browder and his team members, and aimed at undermining the reputation and challenging the integrity of the police and prosecution authorities both in Russia and in Switzerland.”

Journalist Thomas Knellwolf does not buy Veselnitskaya’s assertions that she is just a private lawyer, and has nothing to do with the Russian government. He said the fact that the deputy prosecutor general of Russia organized the meeting between her and Mr. K is proof, in point.

“That shows how close the Russian state and Veselnitskaya are,” he said.

The Swiss Prosecutor’s office tells Fox News “Mr. K.’s” arrest has no influence on any criminal proceedings in connection with the Magnitsky case. But Browder tells Fox he believes it to be quite the opposite, stating: “I think that he is a mole. We were always confused and concerned that the case he was working on—money laundering connected to the Magnitsky murder case—ground to a halt. It never made sense to us until now.” Browder’s company is in the midst of ongoing litigation in Switzerland over Denis Katsyv’s funds.

Browder also thinks “Mr. K.” has compromised the man overseeing his case, and many Russian money laundering cases, Switzerland’s Patrick Lamon. Browder has petitioned to have him removed from his case. Fox News approached the Swiss Criminal Court about this. The court said it cannot comment on an open case.

“I don’t know if Lamon has been compromised,” Thomas Knellwolf said. “But I think it would be a wise and fair decision to remove him from the Magnitsky case.”

To what extent was Veselnitskaya defending the legitimate rights of a commercial client, and to what, if any extent, is the government of Russia trying to influence Switzerland, and turn the state against Bill Browder, and perhaps others fighting Russia in a court of Swiss law? The answers to those questions lie in the ongoing proceedings of a Swiss court.