I've been wondering that for awhile now too.

Despite what Milton said about picking Micah up after Guarma, it’s heavily implied throughout the game that he was a rat the whole time. From the beginning, we’re meant to question whether the Blackwater job was a trap, and Rockstar wouldn’t have planted that seed for no reason. Additionally, Dutch’s wanted poster can be found at Micah’s camp in Chapter 2. Nobody carries around a wanted poster without the intention of collecting a bounty. Meanwhile throughout the entire game, Micah is constantly mentioning the Blackwater money and how they should go back for it, knowing full well that they’d be captured if they tried. It sounds a whole lot like he’s simply trying to lead them back into a trap and collect on Dutch’s capture, or at least strike a deal for aiding in the capture.

Further evidence of Micah’s intentions are implied in a newspaper article after the train heist towards the end of Chapter 2. The law managed to make it there peculiarly quickly, and the gang even questions whether someone talked. Sure enough, the newspaper article about the heist states that lawmen were tipped off beforehand. Nobody else knew about this heist besides a few members of the gang, so that article proves there was a rat from the beginning. Given what’s implied about Micah’s intentions (the wanted poster, the insistence on going back to Blackwater, the fact that he did turn out to be the rat), he’s the most probable one who tipped off the law (and remember, Molly only began acting hostile to Dutch in Chapter 3, so it’s very doubtful she was a rat as early as Chapter 2, if ever).

A final point, and one that’s just conjecture, is perhaps the most interesting. During the heist of the Lemoyne National Bank, every member of the gang is dressed in dark clothing with the exception of Micah, who’s in a full white suit. Compared to everyone else, he stands out greatly, surely enough to stand out in the event of a shootout with the Pinkertons. It’s been theorized that this was done on purpose, and Micah had been talking with the Pinkertons. When the shootout starts, the Pinkertons would be able to identify their inside man because of his starkly contrasted outfit. The Lemoyne bank robbery, just like the Blackwater heist, involved Pinkertons ambushing the gang suspiciously quickly, and once again Micah is the odd one out.

The article about the train heist confirms the gang had a rat from the very beginning. The wanted poster, the white suit, the insistence on going back to Blackwater, all very missable details that make Micah look very suspicious throughout the game. Perhaps we’ll never know the truth for certain, but considering the evidence, it’s very likely Micah was a rat the whole time.

^well damn I sure didn't think about any of that, lol

I think that Micah was the rat, but only after returning from Guarma.

@ClayHamric I would dispute your claim that Micah is “heavily implied throughout the game that he was a rat the whole time”. Firstly, the wanted poster is only for private (effectively self-employed) bounty hunting. If Micah was working for the Pinkertons, then he’d be an employee and wouldn’t get the promised reward; instead, the Pinkertons as a whole would be rewarded for bringing in Dutch and Micah would be paid his employee’s salary - or perhaps spared jail - depending on his arrangement with them if he was an employee. Micah therefore would not carry a wanted poster if he was working with the Pinkertons, so if anything, it disproves that he was working for the Pinkertons at that time. In terms of reasons why he might be carrying it, I would suggest that he was fully aware of what Dutch’s bounty was and had already contemplated the idea of betrayal (as a private bounty hunter getting all the money himself, not as a Pinkerton agent), but simply hadn’t enacted this by that point.

Secondly, the train job. I do not recall seeing any newspaper article stating factually that the heist was a set-up or that the gang were tipped off. Could you tell me which newspaper you found it in? Even more importantly, however, is this: at the time of the heist, Micah was either in jail or camping in Big Valley. He hadn’t seen or been in contact with the gang since the evacuation from Colter (long before the train heist was ever even talked about), so he wouldn’t even know about it. Therefore, if the gang were betrayed, it wasn’t him. Remember that the Pinkertons can find out information through other means than just traitors, hence why they are such a formidable organisation.

In terms of the Blackwater business and Micah’s interest in going back there, it’s a bit harder to come up with anything concrete because details of the heist are, for obvious reasons, not fully known. I admit that Micah’s insistence in pursuing a heist which turned out to be a Pinkerton ambush is a bit suspicious, but I would argue that his personality had a lot to do with it. Micah is a nihilist who loves a big shootout and will always go for something high-risk; the extremely high amount of money offered by the bank job was also likely to have been a motivating factor. Additionally, remember that Arthur and Hosea had their own lead, but given Micah’s dislike/jealousy of Arthur and his intention of proving himself to Dutch, it is perhaps plausible to say that Micah wanted Dutch to pursue the heist in order to prove himself. After getting such a big take, Micah’s logic says, Dutch will be forever thankful for it.

Micah’s determination to return to Blackwater is not suspicious at all, in my opinion. With $150,000 stashed there, it’s no wonder that Micah would intend to collect it. What he’d do with it after that is unknown, but that’s irrelevant. The huge number of Pinkertons in the town would not deter him either, as he is never afraid of large shootouts.

Micah wearing a white suit in the bank robbery is actually a very interesting detail. While it may be coincidence, the amount of detail that Rockstar put into the game would suggest otherwise. The theory about making him stand out seems quite plausible as well, but it could more subtle than that. With Micah’s white hat generally being worn by the “good guys” and lawmen of Westerns, it foreshadows his defection to the law’s side, and the white suit may be a reflection of this in some way. It may also be to make him stand out to the player, highlighting that he is a key character in upcoming events, or perhaps to make him contrast with Arthur’s dark suit. To add to this, Micah’s shirt is a dark red colour, which contrasts with the (vaguely) blue colour of Arthur’s as a way of both highlighting their differences and reflecting how their hats are opposite colours. It could also be to symbolise how the rest of the gang is united in being loyal and true to the group, while Micah is different, having no sense of loyalty or brotherhood and instead being purely self-serving. Finally, it could represent something as simple yet subtle as his complexion, which is paler than the others (blonde hair and blue eyes; he is the only one in the job to have a fully pale complexion like this), which may in turn link back to how he is seen as different from the others in his outlook and future deeds. This last point is certainly very interesting, and I’d say it’s the best argument for him being a Pinkerton the whole time. Nonetheless, I still believe he only became a Pinkerton after returning from Guarma, as Milton says.

@Wagwan piffting23 Blackwater Ledger, Issue No. 63 - Who Are The Scarlett Meadows Bandits? - “It was then that lawmen, having been tipped off to to the robbery, arrived on the scene and confronted the outlaws.”