The National Enquirer kept a safe containing documents on hush money payments and other damaging stories it killed as part of its cozy relationship with Donald Trump leading up to 2016 presidential election, people familiar with the arrangement told The Associated Press.

The detail came as several media outlets reported on Thursday that federal prosecutors had granted immunity to National Enquirer chief David Pecker, potentially laying bare his efforts to protect his longtime friend Trump.

Trump's former lawyer Michael Cohen pleaded guilty this week to campaign finance violations alleging he, Trump and the tabloid were involved in buying the silence of a porn actress and a Playboy model who alleged affairs with Trump.

Several people familiar with the National Enquirer's parent company, American Media Inc., who spoke to the AP on the condition of anonymity because they signed non-disclosure agreements, said the safe was a great source of power for Pecker, the company's CEO.

The Trump records were stored alongside similar documents pertaining to other celebrities' catch-and-kill deals, in which exclusive rights to people's stories were bought with no intention of publishing to keep them out of the news. By keeping celebrities' embarrassing secrets, the company was able to ingratiate itself with them and ask for favors in return.