Police recovered more than 50 guns while executing search warrants following Vance Boelter's arrest. How did he amass that high-powered cache? Senior investigative reporter Jennifer Mayerle went to the Bureau of Alcohol, Tobacco, Firearms and Explosives to better understand the law and to learn what happened to those weapons after they were seized. 

Court documents show what investigators found inside Boelter's Green Isle, Minnesota, home and inside the SUV that resembled a police squad car. The evidence list of guns the Bureau of Criminal Apprehension recovered shows pistols, rifles and revolvers. Inside the SUV they recovered five semi-automatic, assault style rifles. They recovered upwards of 50 weapons in all. 

"Are there any restrictions on how many guns a person can buy?" Mayerle asked.

"No. If you are not federally prohibited, you can purchase as many firearms as your budget allows you to purchase," ATF Special Agent in Charge of St. Paul Field Division Travis Riddle said.

Riddle says the purchase process starts with filling out a "4473 form" inside what's called a Federal Firearms Licensee or FFL, or a store that sells guns.    

"You're going to fill out the 4473, which has a list of questions. Most of them have to do with prohibitors. You know, are you a felon? Are you addicted to a substance? The FFL will also include the firearm information. They'll fill it out, you know, make, model, serial number, caliber, and you're also attesting to the fact that the gun that you are purchasing is for yourself and not for somebody else," Riddle said.

He says as long as the person passes the background check, they can walk out the door with the firearm the same day.

Boelter was legally able to purchase a gun. Riddle says each one investigators seized was traced by the ATF to learn the origin of the gun. 

"So all the firearms that were recovered from the multiple scenes were urgent, traced through the tracing center, and then from that point, the tracing center will initiate the trace, which will go to the manufacturer, to the distributor, to the FFL," Riddle said.

WCCO took you inside the ATF National Tracing Center to show how crime guns are traced. It's where they can figure out who bought the gun, when and where. The information can provide investigative leads. In a case like this, the request is escalated.

"This was our contribution to the investigation. We had people on standby at the tracing center, and we also had people on standby at the correlation center for any of the shell casings so they were ready when that information was submitted to immediately start the tracing process," Riddle said.

Congress prohibits the ATF from sharing gun trace information publicly, so we don't know what the trace information revealed. The agency can only share the data with the investigating agency and prosecution.

The new gun tracing law went into effect Tuesday, following a WCCO investigation. Agencies in Minnesota must now trace all guns recovered from crime scenes and share that information with agencies statewide.