There's been a few statements to that effect from congresspeople, and I imagine they can direct Capitol Police to initiate the efforts even if no other federal law enforcement agency wanted to. But also the FBI has stated that they are seeking any additional info on the people involved:
Of course, they barely need the tips. All the footage available online + phone data should be enough for them to identify hundreds. Basically there's been no definitive one statement of a US Attorney or the like to say that they're going in on this with 100% effort, but its still early.