Robert Mueller — the former FBI director now overseeing the Department of Justice’s investigation into Russia’s election-year meddling and contact with the Trump campaign — has been briefed on the contents of some of the memos that former FBI Director James Comey kept to document his conversations with President Donald Trump, according to a person familiar with the matter.

Additionally, he has already visited FBI headquarters, where he met with the counterintelligence agents who have been working on the case since last July, according to two people familiar with the matter.

In one memo, Comey wrote that Trump asked him to end the FBI probe into former national security adviser Michael Flynn, according to a person familiar with the matter.

One source added that part of Mueller’s investigation is expected to focus on obstruction of justice. In that case, Comey would be a witness and Mueller will likely interview him as part of the probe.