(CBS) — Chicago Ald. Pat Dowell was so concerned about railyard gun heists that last year she wanted to hold a public hearing to question railway representatives.

But she tells the 2 Investigators the federal Bureau of Alcohol, Tobacco, Firearms and Explosives and railyard giant Norfolk Southern “strongly encouraged” her not to go public for fear she would expose serious security deficiencies.

Dowell held off. Now, it’s happened again.

In the latest incident, a half-dozen semi-automatic rifles and 27 handguns were reportedly stolen from a rail car near 77th and Avalon, the 2 Investigators have confirmed.

“There’s no city like Chicago where every major railroad comes together,” says Joseph Schwieterman, a transportation expert and DePaul University professor. “You have dozens of interfaces – that means small yards spread around town that creates some of these vulnerabilities.”

In May 2014, 13 Smith & Wesson rifles were stolen from a freight car near 63rd and State.

In April 2015, more than 100 firearms were lifted from a rail car. Within weeks of that heist a number of the weapons were used in “unrelated incidents throughout the city of Chicago,” according to court filings.

“The perpetrator has the incentive to get rid of the merchandise as soon as possible because it’s traceable, and that means cash is paid, there in the neighborhoods,” Schwieterman says.

The most recent railyard theft occurred Sept. 18th. It was reported to Chicago Police 11 days later — for unknown reasons. No weapons have been recovered. The suspects remain at large.

The railroad, Norfolk Southern, says the “security of our trains and infrastructure is a top priority.”

An ATF spokesman says authorities are still investigating the September theft. He adds the ATF has had success in recovering guns taken in previous thefts and arresting some of those responsible.