Google LLC
Attn: Legal Department – Custodian of Records
1600 Amphitheatre Parkway
Mountain View, CA 94043
In the cover letter I outlined the problem and the desired remedy (shut down the gmail account and preserve IP and other information for law enforcement), and attached two other documents: an annotated printout of the email thread from a prospective victim of the scam (who sensed something was fishy and contacted me through my website) and the local police report I filed to document the attempted fraud in my name.
Someone at Google contacted me about a week later and confirmed that the account was shut down. I don't know if they did anything else regarding preserving data or shutting down any other Google services this person was using.
I also made a report to the FBI’s Internet Crime Complaint Center, although TBH it looks like a black hole that lets the feds say they are "doing something" for ordinary victims.