Reynash
Overview
Reynash can be found trying to pick the lock on a chest belonging to another Fist. Three other Flaming Fist, Manip Bakshi, Fist Debin, and Fist Oriona, are sleeping soundly in their beds while Reynash is busy with the lock on Bakshi's chest.
As he notices the party, he will nervously tell them to get out since the barracks are for Flaming Fist personnel only. By succeeding a Perception Check, the party can notice that he tries to conceal a lockpick while talking to them.
Interactions
Ratting him out
During dialogue, there is an option to wake up the guards in the room to alert them of the thievery. This can be done immediately, or at any later point in the dialogue.
Reynash will quickly run away, and Manip Bakshi will sleepily confront the party about why they are in their barracks. It's necessary to pass a DC 10 Persuasion Check to convince him that Reynash was trying to steal from them; otherwise the talking party member will be arrested or attacked. If passing the check, the party will be peacefully escorted out of the room and gain 650 XP.
Find out about his stash
Passing a DC 15 Intimidation or Persuasion Check, can make Reynash admit to his crime, although he insists that he's no thief and intends to pay it back eventually. If choosing the Intimidation-based option, he will hand over his 
Thieves' Tools set at the end of dialogue.
At this point, there is the option to immediately blackmail him, which makes him reveal the location of his hidden stash where he's storing the stolen goods. Several companions may disapprove of this choice.
Otherwise, inquiring him further about the reason he's been stealing leads him to explain that he needs gold to flee away on boat, since he doesn't feel fit to be a soldier.
If telling him he "seems capable enough" or to "act like a soldier" he will simply end up walking away sulking and the party won't gain anything. (Except, possibly, his Thieves' Tools set; see above.)
If giving him 
300 gp to help him flee, he will be grateful and reveal the spot of his stash willingly. Otherwise, it's also possible to attempt a DC 15 Intimidation Check to gain the same information, though this may grant disapproval from several companions.
The value of the items in his stash is much lower than the 300 gp which can be given to Reynash.
Pickpocketing
You can pickpocket Reynash easily while he's busy with the chest he's trying to lockpick. (Ironic, isn't it?) Walk up to him while crouched to ensure you won't automatically start dialogue. You can also pickpocket him after dialogue, as he sits down on a nearby chair.
His inventory contains:
- 314 gp (or 614 gp if you gave him 300 gp)
Torch- Thieves' Tools (if not handed over to you)
Thief's Stash
The hidden stash whose location Reynash may reveal can also be found without his help. It's at the north-east corner of the rooftop, on a small lookout. It appears as a pile of building stones that reveal themselves to be an illusion once you pass an Investigation Check.
The contents are rather disappointing:
Altogether, the selling price of these items is only a fraction of the 300 gp you can pay Reynash to have the location revealed. The note found within also doesn't contain any useful information.