WASHINGTON (AP) — Several people familiar with President Donald Trump’s transition organization say special counsel Robert Mueller’s team has gained access to thousands of private emails sent and received by Trump officials before the start of his administration.

The investigators did not directly request the records from the transition and may have raised legal issues by obtaining the messages from a separate federal agency.

A transition attorney sent letters Saturday to Congress saying Mueller’s investigation was provided “unauthorized disclosure” of transition records by the General Services Administration. The agency often stores presidential transition records on its computers.

The people familiar with the transition spoke to The Associated Press on condition of anonymity because of the records’ sensitivity. They say the materials included communications from more than a dozen Trump officials, including Michael Flynn.