Special counsel Bob Mueller has teamed up with the IRS. According to sources familiar with his investigation into alleged Russian election interference, his probe has enlisted the help of agents from the IRS’ Criminal Investigations unit. 
 
 This unit—known as CI—is one of the federal government’s most tight-knit, specialized, and secretive investigative entities. Its 2,500 agents focus exclusively on financial crime, including tax evasion and money laundering. A former colleague of Mueller’s said he always liked working with IRS’ special agents, especially when he was a U.S. Attorney. 
 
 And it goes without saying that the IRS has access to Trump’s tax returns—documents that the president has long resisted releasing to the public. 
 
 Potential financial crimes are a central part of Mueller’s probe. One of his top deputies, Andy Weissmann, formerly helmed the Justice Department’s Enron probe and has extensive experience working with investigative agents from the IRS. 
 
 “From the agents, I know everyone has the utmost respect for both Mueller and Weissmann,” said Martin Sheil, a retired IRS Criminal Investigations agent. 
 
 And he said Mueller and Weissmann are known admirers of those agents’ work. 
 
 “They view them with the highest regard,” Sheil said. “IRS special agents are the very best in the business of conducting financial investigations. They will quickly tell you that it took an accountant to nab Al Capone, and it’s true.” 
 
 “The FBI’s expertise is spread out over so many statutes—and particularly since 9/11, where they really focused on counterintelligence and counterterror—that they simply don’t have the financial investigative expertise that the CI agents have,” Sheil continued. “When CI brings a case to a U.S. Attorney, it is done. It’s wrapped up with a ribbon and a bow. It’s just comprehensive.” 
 
 But the team-up between the IRS and Mueller probe could come with political complications. Mueller has already taken some criticism for the number of Democratic donors on his team. Those critiques intensified yesterday, when word leaked that Mueller was coordinating some of his activities with New York State Attorney General Eric Schneiderman, a long-time Trump adversary. 
 
 The IRS, for its part, became a target of conservative ire during the Obama administration for its investigations into Tea Party groups—probes that Republicans called political witch hunts. The complaints about politicized taxmen could begin again, with the IRS joining forces with Mueller. 
 
 A spokesman for the special counsel’s office declined to comment for this story. 
 
 It’s been widely reported that the special counsel’s team is trying to “flip” Paul Manafort, the president’s former campaign CEO, in hopes he will provide evidence against his former colleagues. Former federal prosecutors tell The Daily Beast one of Manafort’s biggest legal liabilities could be to what’s called a “check the box” prosecution. Federal law requires that people who have money in foreign bank accounts check a box on their tax returns disclosing that. And there’s speculation that Manafort may have neglected to check that box, which would be a felony. This is exactly the kind of allegation the IRS would look into. 
 
 These investigations, which are often extremely complex, can take a lot of time. That means the people involved sometimes have to spend significant amounts of money on legal fees. The Daily Beast previously reported that targets of Mueller’s probe—including Manafort—are facing financial strain because of the probe, and that Manafort recently parted ways with the law firm WilmerHale in part because of his financial troubles. 
 
 As special counsel, Mueller is subject to the same rules as U.S. Attorneys. That means that if he wants to bring charges against Trump associates related to violations of tax law, he will need approval from the Justice Department’s elite Tax Division. Trump hasn’t yet named his pick to run the division, which is a post that requires Senate confirmation. At the moment, career officials are helming the division. 
 
 One former Tax Division prosecutor told The Daily Beast that this could cause trouble for Trump. 
 
 “The fact that there is not a senate-confirmed Assistant Attorney General for the Tax Division, and that the Trump people have disregarded it despite warnings as far back as December that they needed to fill the AAG’s spot… shows what a self-created mess the Trump administration has found itself in,” said the former prosecutor, who requested anonymity to speak candidly. “They have no one to keep Mueller and his Brooklyn team honest. They should be concerned about that.” 
 
 The former prosecutor said it could have benefitted Trump if he had an appointee in the division as these proceedings unfold—and that he’s now missed that opportunity. 
 
 “They could have picked any two people in the world,” he added, “and they picked nobody.” 

 Attorney and former FBI Director Robert Mueller, right, arrives for a court hearing at the Phillip Burton Federal Building in San Francisco, Thursday, April 21, 2016. Mueller has been overseeing settlement talks with Volkswagen, the U.S. government and private lawyers for the automaker to buy back some of the nearly 600,000 diesel cars that cheat on emissions tests. Jeff Chiu/AP Robert Mueller, the FBI's special counsel in charge of the investigation of the Trump campaign's ties to Russia, is now teaming up with a specialized financial crimes unit within the IRS, The Daily Beast reported Thursday, citing people familiar with the development. 
 
 The IRS' Criminal Investigations unit is joining Mueller as the Russia probe focuses more closely on potential financial crimes possibly involving people within the Trump campaign. It was not immediately clear how many of the unit's 2,500 agents would take part in Mueller's investigation. 
 
 Martin Sheil, a retired former agent of the unit, told The Daily Beast's Betsy Woodruff that the unit's involvement is a sign Mueller is invested in beefing up a specific rank within his investigative team. Sheil told the publication that while the FBI has broad jurisdiction in counterintelligence and counterterror, "they simply don't have the financial investigative expertise that the CI agents have." 
 
 "When CI brings a case to a U.S. Attorney, it is done. It's wrapped up with a ribbon and a bow. It's just comprehensive," Sheil told Woodruff. 
 
 The unit's agents have expertise in matters like tax evasion and money laundering and the partnership follows a developing trend within the broader Trump-Russia inquiry, which has also seen a closer focus on key players like former campaign chairman Paul Manafort, who resigned from the campaign in August 2016 amid scrutiny over millions of dollars in undisclosed payments for work he performed on behalf of a pro-Russian Ukrainian political party. 
 
 FBI agents raided one of Manafort's homes in Alexandria, Virginia, last month. 
 
 Mueller also recently partnered with the New York state Attorney General Eric Schneiderman with a focus on Manafort's financial transactions. 
 
 The question of President Donald Trump's personal federal tax returns also comes back into focus with the IRS' reported cooperation with Mueller's team. Trump first delayed publishing his returns during the 2016 election, and later refused to reveal them at all, breaking a decades-long tradition in presidential politics and drawing closer scrutiny of his personal financial profile.
– In his investigation of alleged Russian election meddling, Special Counsel Robert Mueller has reportedly teamed up with the agency that brought down Al Capone: the Internal Revenue Service. Sources tell the Daily Beast that the former FBI director is now working with members of the IRS Criminal Investigation Division, which specializes in tax evasion and other financial crimes. It's not clear how many of the division's 2,500 agents might be involved in Mueller's investigation, but the alleged move is seen as a sign that the probe is focusing on possible financial wrongdoing involving members of the Trump campaign suspected of colluding with Russia, reports Business Insider. "The FBI's expertise is spread out over so many statutes ... they simply don’t have the financial investigative expertise that the CI agents have," says retired CI agent Martin Sheil. "When CI brings a case to a US Attorney, it is done. It's wrapped up with a ribbon and a bow." One bonus of involving the IRS could be that it has access to Trump's tax returns—though if the agency does join the probe, it may revive GOP complaints that the agency has become politicized. Mueller has reportedly also teamed up with NY Attorney General Eric Schneiderman to investigate former Trump campaign chief Paul Manafort's financial history, a move that could pressure Manafort into cooperating in the larger probe.