Why?
The FEDs targets would be the financial, administration of the botnets used in the DDOs attacks..
The arrests are to put pressure on the alleged criminals to turn in the others..
The FEDs are after who is controlling the botnets in the DDOS attacks in the long term..
And you will not see the arrests of those for awhile as far as what appears in the press a the FBI can lock that down for 90 days as far as anybody knowing that you are being investigated..