[jwalsh07]

Well, absent probable cause the Constitution is actually in play

If the police have information that a terrorist has just killed an American and they were seen in a white van, is that probable cause to search white vans attempting to leave the area?

And if its not, how do they ever catch the skell?

[NittanyLion]

If the police have information that a terrorist has just killed an American and they were seen in a white van, is that probable cause to search white vans attempting to leave the area?

No. Just like if the police had info the terrorist was wearing a blue shirt they could detain and search all people with blue shirts.

And if its not, how do they ever catch the skell?

Well, I put my ideas down in a post above. I believe it's #168.