Evil Genius 2: World Domination

For this and any of the other "hard" mode difficulty (can be done in any difficulty tbh) achievements for the other Geniuses, there's a simple trick to make this infinitely easier.

When you create a Prison, create a few cells and power them all down. When a wave of Forces of Justice arrives simply tag 1 or more for capture. Now since there's no power going to the cells, the agent will remain on the spot, stood still awaiting to be lead to a cell.
Now because of this, no more waves will ever arrive unless a) you kill or capture them or b) it's objective-specific.
If the agent does get killed or whatever, simply tag a new agent in the next wave and ensure all cells are powered down still.

If you happen to need to interrogate someone while
you have an agent "waiting", there's another little trick.
By having more than one cell you can power one on, a worker will then immediately start to escort the agent to the cell. So if you power on another cell, the other NPC that's awaiting will then be assigned to the next cell. So if you then power down the first cell that the agent is being led to, he will then remain on the spot again.
However once you've captured your specific NPC and you assign them to be interrogated, make sure you power down the cell the moment they leave or the agent thats "waiting" will be led to that cell.

If at any point it messes up, simply deal with the impending wave and tag again. It can be a tad tedious capturing specific objective NPCs but with this method you won't have to deal with never ending waves of increasing difficulty.