For this specific side mission (complete it before Priority: Surkesk), go to the Citadel Embassies and talk to Commander Bailey (point 1).
When to start
After Priority: Palaven
“Aria TLoak has requested assistance uniting mercenary bands under her control.
Speak to Commander Baileys assistant at the Presidium Commons C-Sec station and gain the allegiance of the Eclipse band.”
Terminus Fleet War Asset
Ask Bailey to let you see the prisoner, then go to Presidium Commons and find the C-Sec Outpost (point 5).
Speak to the C-Sec Assistant then to Jona Sederis.
After the dialogue, tell Bailey you will find another solution and go to Docks: Holding Area, Cargo Hold: A.
Speak to Sayn, and tell him that he can take Jonas place.
Go back to the elevator and Bailey will call you to complete the quest.