Ok. I decided to avoid searching all the universe for combat stabilizers to complete the first federal mission, since they're like super rare and I didn't want to waste the day for that. So I took a mercenary mission for some money. Once there the npc said not to kill him but the contractors, and the mission changed. I wanted to go for the original contrat and killed him, result: mission failed. Really? Did I do something wrong or you can't choose who to kill to complete a mission like that?