I agree, its probably a combination of the three. Bronte tipped off the Saint Denis Police Department about the trolley robbery, and I don't see why he wouldn't pass that info on after the SDPD failed to arrest them, or why the Police wouldn't tell them either. Milton tracked the gang from Horseshoe Overlook to Clemens Point because the gang drew attention to themselves intervening in the Gray-Braithwaite feud, so him realising the connection given how little distance there is between Clemens Point and Shady Belle (compared to the other camps) following the gangs actions in Saint Denis isn't that much of a stretch. As for plain clothes Pinkertons, not sure they were used, but I suppose the entire point is the gang wouldn't notice them, especially in the crowded streets.

Its a massive bank, simple

Big family gang need money, bank has money

Bank+robbery=Money

Bank robbery+overwhelm of cops-cash= BUSTED!

The word you’re searching for is (hypothesis) theory is something proven bound to always happen in the same conditions.

I never thought there was a need for a traitor in the Saint Denis situation. Dutch got sloppy, Arthur says as much( "We don't need a mole, we've been sloppier than the town drunk!" Or something to that effect) and it cost him, dearly.

A ***lot*** of people point out Micah's the only one to wear white during the bank robbery, but I mean, Micah's a real big fan of white if you pay attention to his character.

He's unashamedly racist towards Javier and Lenny, calling them horrid slurs (thankfully r* was tactful enough to not let him get away with the big ones), he's the only member of the gang to wear a white hat, I could go on but I mean, we've all played the game here.

I don't think Micah was betraying the gang from the start, he's a long time criminal before he joined the gang so there's no way he could've been working with the law in any form or fashion there.

Pinkertons were at the Boat in Blackwater because it's a federal boat with a lot of federal money, it was a stupid idea to try to rob it in the first place, and Dutch murdering an innocent woman is what kicks everything off in the first place.

More.to the point, if there was ANYONE who betrayed the Van Der Linde Gang in Saint Denis it was Abigail. I know that's gonna piss a LOT of people off, but I haven't been able to figure out a way for Hosea to be the only one caught in that situation, other than Abigail gave him up.

It would be within her character to do so as well, despite what a lot of people might believe. She never explicitly stated that she believes in dutch or trusts dutch or is loyal to him in any sense of the way. The only reason she's there is because John is too pigheaded to leave. That would also be why they targeted her for arrest immediately, because she likely broke some form of terms on the deal struck between Milton and herself. She never commented on Hosea dying to my recollection, but she definitely seemed the least sad about it.

I don’t even think bronte tipped them off. His death would’ve been enough to alarm the authorities as he had them all in his pocket, including the mayor, and the st Denis bank would of been the next obvious target. All they had to do was set up sentries and alert the Pinkerton's when they arrived in town and/or at the bank. After brontes death I would imagine the city would have been on high alert and on the look out for Dutch and gang.