CHICAGO — When street-gang thieves slipped with ease into a Norfolk Southern rail yard on Chicago’s South Side and ripped locks off one train, they likely expected to see merchandise like toys or tennis shoes. What they beheld instead was a gangster’s jackpot: box after box of brand new guns.

The guns had been en route from New Hampshire weapon maker Sturm, Ruger & Co. to Spokane, Washington. Instead, the .45-caliber Ruger revolvers and other firearms spread quickly into surrounding high-crime neighborhoods. Along with two other major gun thefts within three years, the robbery helped fuel a wave of violence on Chicago’s streets.

The 2015 heist of the 111 guns, preceded by one in 2014, and another last September from the same 63rd Street Rail Yard highlight a tragic confluence. Chicago’s biggest rail yards are on the gang- and homicide-plagued South and West sides where most of the city’s 762 killings happened last year.