COLUMBUS, Ohio (WCMH) – The investigation into Tuesday’s Brooklyn subway shooting has traced a lead on the suspect back to central Ohio.

Investigators found the handgun on the scene and the ATF was able to trace the serial number back to a pawn shop in Columbus.

Sources tell NBC News that the suspect, Frank James, purchased the gun in 2011.

The name of the pawn shop has not yet been released.

Former FBI Agent Harry Trombitas said since there was a serial number on the gun, it must’ve been purchased legally, meaning a background check was done.

Trombitas said James’ true connection to Columbus is still unclear, but this lead will help agents find people who may know a little more about him.

“That’s one of the things the FBI is really good at,” Trombitas said. “We have agents all over the world, certainly all over the country and so if we develop a lead in Columbus, Ohio, our agents in Columbus will be following up on that and conducting an investigation.”

Trombitas said this is not the first domestic terrorism case where a suspect has a connection to Columbus.

He said they will use every piece of evidence collected on the scene as well as social media posts to figure out exactly why James did this.

Trombitas said social media will be a very powerful tool to find out more information, referencing posts James made on social media indicating something was wrong.

“The fact that he was giving some indication that he was upset and it sounds like to me he was on what we call the pathway to violence,” Trombitas said. “We need people to speak up on that. And then, second of all, he was well prepared and knew exactly what he wanted to try to do.”

The handgun was not the only weapon used in this attack. Trombitas said investigators also found fireworks, smoke bombs, and a hatchet in James’ bag.

Trombitas said it looks like James planned out this attack well in advance.

“This individual did some planning,” Trombitas said. “He knew what he was doing. He certainly brought a firearm. It sounded like he had an extended magazine able to fire a fairly large capacity of rounds, 30 rounds maybe. He also had what I would call a tool kit.”

He said the next step is finding out why James bought the gun to start with and what he was doing in Ohio.