For a gun to be traced to a crime it has to have been fired and the bullet or cartridge case recovered. From that, the last official owner can be identified and squeezed for information. If you are the last identifiable owner, the pressure will be intense to prove you are the criminal or to get you to provide the name of the person you gave or sold the gun to. Your unwillingness to cooperate will be considered evidence you are either part of a criminal conspiracy to commit the crime or an accessory to the crime.
When the police have a name, they can start focusing on that person. They can start matching other evidence found at the crime. They can start matching that person's known movements to establish if that person was in the vicinity of the scene of the crime on the date and time of the crime.
When the suspect is interviewed and asked to comment on the evidence collected, many times it is the suspect's lies that cement the case.
All it takes sometimes for the case to "gel" is a name. Remember the Unabomber? His brother provided the name.
In my county an eight year old girl was kidnapped, sexually abused, and murdered. The police and sheriff were stymied for close to two months. They didn't even have a body. When the body was discovered in another county, they still didn't have an idea on who did it until the killer's sister who lived near where the body was discovered called and said, "I think you better have a look at my brother. He molested me when we were children."
Without help from the sister, the police and sheriff may never have caught the killer.
All it takes is a name.
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Bruce Stanton
CDR, USN-Ret.
Sgt., Kings Co. Sheriff - Ret.
