Tropico 5 - Penultimate Edition

I tried doing this on a Sandbox game I'd been playing through every era and had to give up as my police simply weren't catching criminals quick enough in my huge city and 1000+ population.

To do this I started a sandbox game in the modern era with unlimited money and very low economic/political difficulty.

Build two Supermax prisons (for some reason I can't find Dungeon as a building option) either side of a Police Station. Unpause time and invite foreign workers for every position in the Police Station and both prisons. Once you have workers, enter your Almanac via LT+X and find the page that tells you about your citizens by using LB or RB. Select the Homeless category, then Illiterate. There should be quite a few right at the start of the game as there's only four houses on the map and no education facilities. Simply go through the list one by one and select to arrest each citizen. Once you get to 30 arrests issued the game will stop letting you arrest people as the Supermax Prisons only hold 15 prisoners each. Unpause time and let our police get to work. Keep checking the prisons to see how many inmates they have and if people get released before the achievement pops, simply have your police arrest more citizens.

Surprisingly annoying, even in sandbox mode with unlimited money.

The issue is you need to have 20 people in jail all at once. You can't just click arrest on 20 people and this pops. People don't actually stay in jail for very long, so by the time the 10th person of the 20 has been arrested and lead to jail, 5-7 people have already gotten out.

To fix this, you'll need to have a lot of jails, and a lot of police stations, that way the total number of people you can arrest at once will go up, and so will your odds that 20 people will be in prison at the same time.

I ended up having 4 Supermax Prisons, and 2 Dungeons, before I had the 20 total in jail at the same time. It's also good to have a Ministry of Information fully upgraded, as arresting all these people will raise your chances for rebel attacks, and uprisings. I also put a line of Guard Towers near my palace, in case an attack got through.

Works! I would recommend building at least 5 police stations, and more than 3 supermax prisons / dungeons, also build it all together, prisons next to police stations, it's more difficult if you try it with a lot of population, better start a sandbox game!