 Complete the following phrase:  In recent years, politicians and gun control advocates have claimed tracing ghost guns used in crimes may be harder than tracing their commercial variants. This argument is made when assessing ATFs ability to use the serial numbers of firearms associated with crimes to perform trace requests through The National Tracing Center NTC, a division of the bureau that provides investigative leads for local, state, federal and foreign law enforcement agencies. However, ATF NTC uses other technologies and forensic expertise when serial numbers are not present, or have been altered or obliterated from firearms, and local detectives, prosecutors and U.S. Attorneys have many other resources and investigative powers aside from NTC when working gun crimes, including the NIBIN. Additionally, as was seen in 