How to catch a cracker in the US?

[Markus]

Hi,

I'm an ISP in Germany and a cracker (not a hacker :) ) has targeted a 
customers of mine in the last days. The cracker was successful and 
caused financial damage / was successful with data theft. I set a trap 
and finally caught his real IP address - a Comcast user in the US (100% 
not a proxy or bot). What would be the next steps to pursuit him? If I 
contact local authorities here in Germany I'm afraid months will pass by 
and Comcast will have possible already deleted their logs by then (?). 
Any advice?

Thank you!
Markus