I tried google.
https://www.atf.gov/resource-center/docs/undefined/etrace-fact-sheet-june-2020/download
eTrace is a web-based application that is used to track the purchase and/or history of weapons used in violent crimes. The system, available in both English and Spanish, is key in generating leads to help solve violent crimes across the country.
These leads help law enforcement agencies quickly identify potential gun traffckers and suspects in criminal investigations.
Using eTrace, crime guns can be tracked from their original manufacturer or importer, through the wholesale/retail distribution chain, to the frst person who bought them.
The data in eTrace comes from local, state, federal, and international law enforcement agencies.
Authorized users can search eTrace using a variety of felds including gun serial number, type of crime, date of recovery and names of individuals involved.
In addition, participating law enforcement agencies can opt to share frearms trace data with all other eTrace users in their state. eTrace thus allows its users to detect patterns of violent crime across jurisdictions.
#
I can see how comparison may be used here.