Break Manson and Franc out of prison.
Speak to Jacob the Chemist and tell him you don't like the super mutants. He will tell you to break their friends out of jail. Go there and wait. Eventually, the super mutant standing guard will wander towards the door. At this time, you can pick the lock of the cells and free the two convicts. You can also Steal the key from the guard, and use it on the door when he leaves. Either way, you have to wait until the guard leaves to free them, as when the nearby guard stops you.
The quest can also be passed by simply killing all four super mutant guards and using the guard key on their cell doors. Jacob will chastise you a bit for killing everyone but will soon assure you "it doesn't matter."
You have to take this quest before you report about missing people in quest; Find the missing people for Marcus. or the conspirators won't talk to you anymore.
Thanks to you, the anti-mutant conspiracy goes on, and your karma takes a hit. This also opens up the quest to blow up the mine's air purifier.
Once you receive this quest, you can instead turn Jacob in to Marcus for 2500 xp. Alternatively, you can perform the break, then turn them in to Marcus.