EAST RIDGE, TN.  (WRCB)  --  New details in the case against Jesse Mathews, the man accused of killing a Chattanooga police sergeant.

Court records, show Mathews traded three stolen firearms for an assault rifle the week before the botched robbery that led to Sergeant Tim Chapin's death.

Mathews, a convicted felon, purchased the weapon at a R.K Gun Shows in Chattanooga on March 27th.

Since the shooting death of Sgt. Chapin, the ATF has been working to determine who sold Mathews the gun.

Saturday R.K Shows is back in town, and its owner is opening up about the sale that put his organization under the microscope.

Despite federal court affidavits showing Jesse Mathews traded three stolen firearms for an M-4 assault rifle inside the R.K. Shows at the Chattanooga National Guard Armory the weekend before the shooting, Rex Kehrli maintains his show is not a fault.  The owner says the only person who broke the law is Mathews himself.

The signs outside Camp Jordan Park and Arena proclaims welcome to R.K. Shows.  "Same as always," says shopper Jim Perry.  "It looked like a well run gun show". 

Two months after the U.S. Money shooting death of Chattanooga Police Sergeant Tim Chapin, heavy traffic streams in and out of the same show where accused killer and convicted felon Jesse Mathews traded stolen firearms for the assault rifle used in the robbery.

"The only person that broke any laws in the situation would have been Mr. Matthews," says Kehrli. 

Acting on a tip days after the shooting, Channel 3 confirmed Kehrli, the shows owner, was cooperating with the ATF as it investigated whether 25-year-old Mathews purchased the assault rifle illegally at his show.

"This Mathews I'm sure he must have misrepresented who he was," Kehrli says. 

Our camera's weren't allowed inside the Camp Jordan Arena Saturday, but Kehrli did agree to talk over the phone.

Reporter: Do you feel your vendors or your show was at fault in how Mathews obtained the rifle?

Kehrli: No, I don't. 

The show owner says he handing over records to ATF agents days after the shooting.  He says licensed vendors inside signs contracts to follow state and federal laws.

"They will call your name into a federal background check," Kehrli says.  However, when it comes to deals struck by private sellers inside and outside the show, Kehrli says the problem goes back to Tennessee law.  A fact Chattanooga Assistant Police Chief, Tim Carroll, spoke of after the shooting.

"I've got to ask you one question," Carroll says.  "Have you been convicted of a felony?  If you say no, I don't have to check that.  I'm talking about as an individual.  You give me the money, I give you the gun and you walk out the door.  There's no paperwork."   

Since the shooting many details of Mathews, his family and their criminal histories have emerged, exactly how and who sold the 25-year-old the gun we still don't know.

Kherli says he does encourage private sellers to keep records, even providing them with forms to fill out.  Channel 3 also learned from ATF Saturday their investigation as to how Mathews obtained the rifle and whether R.K. Shows is at fault is ongoing.

By law if it was a private sale, the seller would not face charges.  Either way, because of his record, Mathews was not allowed to own a gun.