CNN– Federal prosecutors investigating former President Donald Trump’s handling of classified documents are pressing multiple witnesses for details about their attorneys, including whether any of them have attempted to influence testimony in order to protect the former president, multiple sources tell CNN.

Investigators have focused these questions toward a group of witnesses who either work for Trump or are represented by lawyers provided by him. In some instances, prosecutors have asked how witnesses found their lawyers and if they know how they were compensated during grand jury sessions.

The line of questioning about Trump-provided attorneys suggests prosecutors are looking at any efforts by the former president to keep control over more than two dozen Mar-a-Lago staffers and political aides who have become central witnesses in recent months, and whose legal bills are paid by Trump. Investigators working for special counsel Jack Smith are exploring multiple facets of a possible obstruction case, and that could include whether testimony has been improperly influenced and coordinated within Trump’s legal network.

No one has been charged with any crime in the federal documents probe. Yet prosecutors in recent weeks have moved aggressively to lock down witness testimony in the grand jury and have gathered significant documentary evidence that has moved them toward potentially making a case, according to one of the sources.

“They wanted to know who’s paying, how did they invoice?” said one person familiar with the matter, referring to questions prosecutors have asked. Prosecutors asked witnesses questions like “‘Did they tell you what to say? Did they get you to alter your testimony?’” The source said. “Even if it were true, would anybody admit it?”

Many of the defense lawyers representing these Trump-aligned witnesses have been paid by Trump’s Save America PAC.

By the end of 2022, Save America had paid $16 million for lawyers who defend Trump himself and people who work for him in the ongoing probes and in response to other legal issues, such as Trump’s recent indictment in Manhattan and an upcoming trial opposite columnist E. Jean Carroll.

The PAC, which was set up days after the 2020 election and solicited millions in donations with baseless claims of election fraud, also keeps a handful of Trump staffers on its payroll, too. Several of Trump’s closest aides who are also now witnesses remain on his payroll and also receive hefty consulting fees through Save America PAC.

It’s not unusual for deep-pocketed organizations to bankroll lawyers for their employees who need legal help to respond to criminal probes or lawsuits. Attorneys for several of the Trump witnesses have maintained that no matter where their funding comes from, the advice they provide to their clients is to protect them individually.

Yet the Save America spending has caught the interest of special counsel investigators. Prosecutors have asked similar questions about Trump-provided lawyers as part of the parallel probe into January 6 and the effort to overturn the 2020 election, and even subpoenaed consultants who received Save America disbursements to trace the spending.

In testimony to the House January 6 committee last year, former Trump White House aide Cassidy Hutchinson said that a Trump-backed attorney had tried to coach her into not sharing information to protect Trump. She eventually switched lawyers before providing extensive testimony to the committee and to the criminal investigators looking into January 6 and Trump.

In comments last week following his indictment in Manhattan, Trump made references to those in his inner circle facing questions from federal investigators, saying “the people who work for me” were being harassed.

“We have this Jack Smith lunatic threatening people every day through his representatives. They’re threatening jail terms, but talk about Trump and you’ll go free,” Trump said in his speech hours after pleading not guilty to the business-related charges brought by Manhattan District Attorney Alvin Bragg.

Peter Carr, a spokesman for Smith’s office at the Justice Department, declined to comment.

CNN previously reported one aide close to Trump, Walt Nauta, had told the FBI about Trump directing that boxes be moved out of a storage room at Mar-a-Lago after the Justice Department subpoenaed all classified records in his possession. Nauta, who serves as a body-man to the former President and even traveled to New York with him for his arrest last week, initially denied handling the boxes but was captured on surveillance footage. Nauta’s attorney Stanley Woodward declined to comment.

In recent months, a Mar-a-Lago employee who helped Nauta move the boxes has spoken to investigators, sources familiar with the probe say.

Smith’s team also took aggressive steps to capture the grand jury testimony and notes of Evan Corcoran, one of Trump’s primary defense attorneys who responded to the subpoena, and have interviewed other attorneys on the team as well.

In the past, Trump’s use of lawyers to do his bidding and keep people close to him in the fold has attracted extensive, repeated inquiries from prosecutors.

In the Mueller investigation, prosecutors found that lawyers for Trump put public and private pressure on a handful of top advisers, including Michael Flynn, Michael Cohen and Rick Gates, as they considered plea deals to cooperate in the investigation.

CNN’s Kristen Holmes contributed to this report.