After finding the "NPD" mission from Avon Lady's site i thought about messing around with police missions like that.
Oh, can the main character, John Edwards, speak to the dead? You know, John Edward, his show Crossing Over on which he speaks to the dead? Sorry, couldn't resist. ;D
Anyways, back on topic. I like the idea of having your guy recruiting and investigating but the rest of the plot sounds like a action movie. To me it doesn't sound to realistic, kind of cheesy. I don't think you could could a big story out of that.
If i were doing this i would have the campaign revolve around a meeting of delegates from around the world. A few missions could involve the gang you mentioned and they have connections to some terrorist type group/s. Toward the end all hell could break loose and you and the other officers have to protect the delegates and such.
A whole police campaign would be good but it would need a good, in depth story, and good dialogue.
I am an aspiring writer so i tend to analyze the hell out of the stories for missions/campaigns. ;D Some just have unrealistic and stupid stories and even worse dialogue. When campaigns have characters most of the time all the characters talk the same. None are distinctive in the way they talk.