(OBVIOUS SPOILERS) Question about the final mission's story

[Panzer]

So I'm really simple minded and it's very common for me to struggle to follow the story in most games. Which is likely why I absolutely SUCK at interrogations in this game.
I just have a question for the final mission, "A Different Kind Of War." To my understanding, Ira was the man who charged into the cave back in Okinawa, on Cole's command. And he was found to be the man behind all/some of the Arson cases, as Jack found in Ira's shack. (I think Ira is his name, I can't really remember) But on the way to the sewers, why is Jack chased by police? What did I miss?
I understand that the police chase Herschel and Cole because they're helping Jack, but why are they chasing Jack in the first place, when he's an investigator too? And who is this Petersen dude, that halts the police outside the sewer entrance? Also. My game decided to not save, I even made it through the credits and ending cutscene to the main menu, and I quit but it didn't save. I think I quit too early, so I have to go through the emotional pain of this mission all over again :,)

[Andraboy]

Peterson is the assistant DA guy, the one who visits Jack Kelso when he was hospitalised after the mafia beats him the previous night. He claims he wants to take the DA's position because the current one is corrupt and he needs Jack's help to do so. But in the end he became corrupt himself when chief police warren offered him a deal at the entrance of the sewer tunnel.

As for why Jack was chased, i am also confused lol

And i think the game was supposed to not save at the last mission. So anyone who clicks resume after the end credits will be brought up at the beginning of the chase

[TheCaptain]

i assume police are after them for attacking Leland Monroe in his mansion