Thomas Caldwell once told a federal agent that selling guns was an addiction.

Even after being told to stop because he had no license, the Wisconsin man kept peddling firearms, posting more than 200 ads on a controversial website.

One of those guns, a Glock 26 9 mm handgun, ended up in the hands of a four-time felon who used it in February to kill Chicago police Cmdr. Paul Bauer in a shocking daylight shooting in the heart of the Loop, according to recently filed federal documents.

The records give a rare look at how shadowy gun deals flourish between private owners and over the internet — how easy and lucrative they are. And how lethal they can be.

“I’m not surprised that gun changed hands and came from out of state,” said former Chicago police First Deputy Superintendent John Escalante, Bauer’s childhood friend. “I think they (gun sellers) don’t want to think about that. They are seeing the bottom line, which is money in their hands. If that gun winds up being used to shoot someone, they’re thinking, ‘Well, I didn’t shoot the guy. I didn’t pull the trigger.’ ”

The Chicago Tribune reported in March how the gun — known as a “Baby Glock” for its compact size — made its way from a gun shop near Madison, Wis., to Lower Wacker Drive in Chicago. Now the open and unregulated market that carried it into Chicago has come into sharper focus as federal charges have been filed against Caldwell and a second Wisconsin man, Ron Jones.

Tracking the ‘Baby Glock’ that killed Cmdr. Bauer: A Wisconsin shop, a gun club and a shadowy sale on the internet »

Agreed to stop selling guns

In the hours after Bauer’s death, the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives traced the Baby Glock to a man who bought it from the gun shop in December 2011, according to federal records reviewed by the Tribune. From there, the investigation led federal agents to Caldwell. But this wasn’t the first time he had appeared on the ATF’s radar, court documents show.

Caldwell first drew the agency’s attention in June 2015 when Milwaukee police found a Glock 29 10 mm pistol while serving a search warrant at a felon’s home during a narcotics investigation. Police ran the gun’s serial number through a national law enforcement database and learned that Caldwell had bought the firearm the day before from a licensed dealer.

In a video obtained by the Tribune, Shomari Legghette is taken into custody on Feb. 13, 2018 after the fatal shooting of Chicago police Cmdr. Paul Bauer outside the Thompson Center. In a video obtained by the Tribune, Shomari Legghette is taken into custody on Feb. 13, 2018 after the fatal shooting of Chicago police Cmdr. Paul Bauer outside the Thompson Center.

Four months later, the ATF conducted what it calls a compliance inspection of the dealer and learned that Caldwell had bought 41 guns from him in a year. The agency also discovered that Caldwell had had no reportable income since 2012.

Sometimes the dealer would have several handguns to sell to Caldwell, according to the ATF. But Caldwell would buy only one of them at a time, every six days, to get around a federal requirement that the dealer report the purchase of two or more firearms by the same buyer within a five-day period, according to court records.

“I didn’t think I was doing it as a business,” Caldwell said during a court hearing last month in Madison while pleading guilty to a federal charge of selling firearms without a license. “I thought it was legal, but it was brought to my attention it was illegal.”

Caldwell, 68, told the ATF he was paid about $21,000 each year in Social Security and disability checks. He bought about 30 to 40 guns a year, spending roughly $2,000 a month on them. He sold the guns he didn’t like through armslist.com — a website that connects buyers and sellers of weapons without requiring registration, proof of identity or background checks.

When the ATF asked Caldwell about the gun seized in Milwaukee, he said he had no record of it in a notebook he kept of his firearm transactions.

By the end of 2015, the ATF served Caldwell with a letter warning him to stop selling guns until he got licensed.

“Mr. Caldwell signed the warning letter, and he told (an ATF agent) he would stop selling guns,” Assistant U.S. Attorney Timothy O’Shea said during the hearing last month. “He didn’t want to be in trouble.”

In 2016, Caldwell filed for bankruptcy. He listed among his assets 47 guns — 24 rifles, 22 handguns and a shotgun — worth a total of $9,300.

Baby Glock reaches Chicago

Caldwell had bought the Baby Glock in March 2015 for about $350 from the man who had purchased it from the gun shop outside Madison. The two belonged to the same gun club. Two years later, Caldwell sold it to a Milwaukee man named Ron Jones — whom Caldwell knew as “Kevin Sweepee” — over armslist.com, according to federal authorities.

The two had done business before, further evidence of the extent of Caldwell’s gun selling.

Caldwell told the ATF that Jones bought at least 15 guns from him over a five-year period. Jones was once arrested on felony drug charges, but they were later dropped. Jones told federal agents he spoke by phone with Caldwell about three times a month about gun sales.

The Baby Glock appears to have landed on the streets of Chicago by the summer of 2017, about two months after Caldwell sold it to Jones. Shell casings found at the scene of a Loop shooting on July 10 that year were traced to the Glock.

A man was sitting in a car at Garland Court and Lower Wacker Place — just blocks from where Bauer was shot months later — when he was shot in the side. The man, 33, told police someone in a passing black sedan shot him, but he changed his story and then refused to cooperate, a source said.

No charges were filed, and it’s unclear how the gun got into Chicago.

Meanwhile, Caldwell continued to sell firearms in Wisconsin, and the transactions once again caught the attention of the ATF.

Armando L. Sanchez / Chicago Tribune Slain Chicago police Cmdr. Paul Bauer's name is etched into the police memorial wall outside Soldier Field, shown on Oct. 9, 2018. Slain Chicago police Cmdr. Paul Bauer's name is etched into the police memorial wall outside Soldier Field, shown on Oct. 9, 2018. (Armando L. Sanchez / Chicago Tribune)

In fall 2017, Madison police confiscated a Taurus 9 mm handgun from a reputed drug trafficker. Police traced it and discovered that Caldwell had bought the gun just two weeks earlier. ATF Special Agent Michael Klemundt, a former Chicago police officer, conducted a background investigation and learned that Caldwell still was not licensed as a firearms dealer.

Caldwell had posted 202 ads for gun sales on armslist.com after getting the warning letter, the ATF found. He also had bought at least 95 handguns and 11 rifles from nearly 60 different sellers during that time. At least 11 firearms recovered during police investigations were traced back to Caldwell between 2004 and 2017, according to court documents.

In December 2017, ATF agents, working undercover as part of their investigation of Caldwell, met him at his Madison home and bought a Walther P99 .40-caliber handgun for $500. The meeting was arranged through armslist.com.