Ha. I assumed you had to pick them up. I also assumed you got money for it. See, what happens when you assume…

did u do it in multyplayer?
i catched 2 ghost in singleplayer in one trap!
it works like this:
thow a trap, catch a ghost, wait till the yellow laser appears againcatch a 2. ghost!

I remember the GameInformer article about the game. One of the developers said that you can freeze a Ghost and then “kill” it by blasting it to pieces with the Dark Matter Generator's secondary function, but they said that doing that doesn't get you as much money as if you were catching the ghost.

So it looks like they were originally going to have you gain more money to upgrade your equipment, but it seems that they dropped the idea later on and gave more depth to trashing the level and having Peck or the city pay for all the damage.

Weird…