Story highlights Mueller already visited FBI after being named special counsel last week, per sources

Source: Mueller will likely want to talk to people involved in House and Senate investigations

(CNN) 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.

Potentially complicating that effort is Comey's acceptance to testify on Capitol Hill after Memorial Day. The source says Comey likely will be limited with what he will be able to say now that the Russia probe is in the hands of Mueller.

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