Judicial sources told AFP that the federal prosecutor would hold a news conference later Monday.
Afweyne announced in Mogadishu in January that he was quitting piracy after a highly profitable eight-year career. He said he was working to persuade other pirates to do the same.
Described last year by the UN as "one of the most notorious and influential leaders" in Somalia's pirate hub, he notably was involved in the 2008 capture of the Saudi-owned Sirius Star oil supertanker, released for a ransom of several million dollars.
He also reportedly took part in the 2008 capture of the MV Faina, a Ukrainian transport ship carrying 33 refurbished Soviet-era battle tanks, which was released after a 134-day hijack for a reported three million dollars.
Belgian media said he was suspected also of the 2009 capture of a Belgian ship, the Pompei, held for over 70 days.