Suspected Synth

Suspected Synth (displayed as Suspected Synth at (Location Name) is a Minutemen radiant quest in Fallout 4.

Detailed walkthrough
This quest can be periodically obtained when entering an owned settlement. As the Sole Survivor nears the settlement, they hear a commotion. A settler has been accused of being a synth and is being held at gunpoint by another settler, while a third defends the accused. It is up to the Sole Survivor to decide the fate of the accused. There is a 50/50 chance that the accused is actually a synth, but the only way for the Sole Survivor to know for sure is to interrogate them (a hard dialogue check) or kill them and check the corpse for a Synth component.

Regardless of any successful interrogation, the Sole Survivor has several options:
 * Tell the settlers to back off and let the accused live (results in the accused being spared)
 * Tell the settlers to kill the synth (results in the accuser killing the accused)
 * Tell the settlers to decide (also results in the accuser killing the accused)
 * Leave the settlers alone (results in the accuser killing the accused within 24 hours)
 * Kill one of the settlers (see last paragraph)

If the accused is spared (regardless of whether they were actually a synth), the settlers will return to their duties after a short dialogue. If the accused is killed by the accuser, the accuser and the defender will examine the body before returning to their duties.

If the Sole Survivor elects to kill the accused themselves, the accuser will become hostile. At this point the Sole Survivor can kill the accuser, or simply hide until the accuser ceases hostility. The Sole Survivor can also kill the accuser first. This will make the accused hostile, and the quest cannot be completed until the accused is killed (even if the accused ceases hostility). Killing any other settler makes the whole settlement permanently hostile; the only way to complete the quest at this point is to kill the accused.

Bugs

 * It is possible to walk into the settlement to find the objective suspect already dead, which seems to make the quest impossible to accomplish as the quest marker will hover above the dead suspect.
 * To fix this, you must reload a previous save and quickly go to the settlement before the synth is killed.
 * Even after the conflict has been resolved, if the player character kills the accused settler, the settlers repeat "I guess he (or she) wasn't a synth after all" but become hostile nevertheless. The same can happen if the player character attacks the settler along with the accuser.
 * To fix this, reload a previous save.
 * It is possible for the accused to be dead later on even if you chose to spare them. In such a case, at 6:20am the day after being accused, the suspect will fall dead (as if the console kill command was used). If the accused was not a synth and the settler who defended the accused sees the body, they will spend a few seconds inspecting it, then say "She wasn't a synth. Goddammit! You murdered her!" All companions in range of this will react.
 * To prevent the murderer accusation, don't allow the accused's friend to see the body. This can be done by opening the console, targeting the body, then entering "disable." If the body disappears, continue with "markfordelete." If the body did not disappear, something other than the body was selected. Enter "enable" to re-enable it, then try targeting again.
 * Reloading a save from the first instant voices are heard, then fast-travelling away may prevent the quest from being assigned for that instance, as the quest is set to stage 500.
 * If the suspect was in dialogue when the quest was triggered (for instance, introducing themselves as a new settler), the quest will bug and the player character won't be able to speak with them to start the interrogation.
 * The quest may randomly fail at any stage due to a bug in the script. Reloading a save and trying again will sometimes allow the quest to be completed.