This is literally the first time I have run into a lib claiming the FBI stats are no good.
No one is making that claim!
Read and learn!
Sources of Crime Data Uniform Crime Reports and the National Incident-Based Reporting System National Institute of Justice
Sources of Crime Data: Uniform Crime Reports and the National Incident-Based Reporting System
Two major sources of crime statistics commonly used in the United States are the Uniform Crime Reports (UCR) and the National Incident-Based Reporting System (NIBRS).
Uniform Crime Reports
The UCR is the FBI’s widely used system for recording crimes and making policy decisions. It has tracked data on seven crimes since 1930: murder, robbery, rape, aggravated assault, burglary, theft and vehicle theft. In 1979, the UCR started reporting on arson. Nearly 17,000 law enforcement agencies report UCR data to the FBI
but those data have several limitations that make them unsuitable for analyzing local crime.
National Incident-Based Reporting System
Crime data from NIBRS (as of 2004) come from 5,271 law enforcement agencies that represent
about 20 percent of the total U.S. population. NIBRS is the result of the FBI's efforts in the 1980s to revise the UCR.