Back when the Irish were considered an 'other' and like vampiric monsters sucking all the jobs out of America, there was a period where they slowly started working as pigs (cops) because nobody else wanted to do that bullshit at first.
So when criminals were loaded up in a carriage, the wagons were called 'paddy wagons' due to cops mostly being Irishmen and back in Britain paddy was a slur for an Irishman.
I do apologize for my fellows for being pigs.
Maybe this is common knowledge? I'm not sure.
One of the big reasons the Irish ended up working as cops is because they were a large voting block but they didn’t really vote. So in order to court their votes, democratic politicians promised them jobs. However when the time came they couldn’t convince any employer to hire them because of anti-Irish and anti-catholic prejudice so the only way they could deliver on their promise was to use the only employer they had some control over - the police.
The Irish Way: Becoming American in the Multiethnic City by James Barrett goes into more detail on this.
There also used to be anti-Catholic conspiracy theories that the Irish were secretly planing to take over American cities through a secret plan the Vatican had given them.
Critical support for comrade Pope.
It also has a bit to do with timing, by the time Irish people were being given jobs in the police other immigrant groups were starting to become more prominent in a lot of US cities and prejudices slowly moved away from anti-Irish to other groups. You see similar in the UK with Caribbean immigrants becoming a lot more accepted into society by the time large scale immigration from Asia became the next big racist bugbear.
…the Jack Chick conspiracy theories?