There's a bit more information from Sarah Jeong, who has been covering this for Forbes:

"Amazing moment later today: in affadavit, DHS agent referred to @a_greenberg's interview of DPR and said it sounded like Mark Karpeles." [1]

"Investigation found that Mutum Sigilum, a Karpeles holding, had registered http://silkroadmarket.org #SilkRoadTrial" [2]

"Karpeles's attorneys met with Baltimore law enforcement, offering to give up the identity of DPR if Karpeles was not charged w crim charges" [3]

[1] https://twitter.com/sarahjeong/status/555844940841115648 [2] https://twitter.com/sarahjeong/status/555821164661321728 [3] https://twitter.com/sarahjeong/status/555821577485713412