In one of the Baccano! episodes (apparently episode 8, according to Wikipedia), we see a number of people from the police being briefed about the burglaries committed by Isaac and Miria. Does the pair actually end up getting confronted by law enforcement anytime in the course of the anime series (or even the light novels)? I don't recall this happening in the anime, but I have read that it leaves out some details from the light novels.
Some undercover cops over hear Issac talking in the Alvaere about their various crimes (in 1934) and asks him and Miria to come see a show at a nearby building. Issac asks Miria to go fetch his wallet, and then tells the police officer to go ahead and arrest him. Due to being in the middle of Martillo territory with a lot of the gang glaring at them, they decide to only arrest Issac instead of making a scene trying to capture Miria, who is then sent to stay with Jacuzzi's crew at the Genoard vacation manor to lay low until the charges against her are dropped, where she remains until she goes to meet Issac after his release.
Victor pulls some strings and agrees to drop the charges against Miria and give Issac a reduced sentence if he'll help them with Huey at Alcatraz. Since Firo agreed to go to prison in exchange for Victor not pursuing his vendetta against Ennis for devouring his friend (and being involved with Szilard's schemes), they decided not to use Issac and he simply did his time (3 1/2 months), and was released, and then he and Miria had a clean slate.
Due to the ridiculousness of all the crimes, the only crime Issac was actually charged with was robbing the Genoard mansion.
In the eighth novel (year 1934), Firo is sent to Alcatraz by Victor Talbot and meets both Isaac and Ladd Russo there. Isaac was imprisoned for various thefts but is released in the same year.
This is the only known sentence and it's not known which thefts, but I recall from the anime that the police knew most of their criminal actions. I don't know why he was released the same year or why Miria wasn't in prison, though.