CHICAGO (CBS) — Violent crimes and thefts on the CTA dropped by more than a third in the first half of this year, compared to the first six months of last year, city officials said Tuesday.

The CTA said thefts were down about 20 percent, and robberies were down 35 percent for the first six months of 2014, compared to 2013. The mayor’s office said violent crime was down more than 34 percent overall.

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The CTA credited its increased use of surveillance cameras for helping spur the drop in crime on its buses, trains, and platforms. The CTA has more than 23,000 cameras on buses, trains, and rail stations. The agency also pointed to increased police patrols and undercover operations.

Mayor Rahm Emanuel and CTA officials were expected to provide further details on CTA crime data later Tuesday.

Surveillance cameras recently played a vital role in tracking down and arresting two men who held up an Orange Line train in broad daylight on July 16.

Michael Taylor, 20, was charged Sunday with four counts of armed robbery and two counts of aggravated assault with a firearm. Taylor was arrested Friday night in Rockford. In addition to the Orange Line robbery, Taylor also was charged in connection with a May 12 shooting on the 5700 block of West Ohio Street, in which no one was hurt.

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A second suspect was being held in Gary, Indiana, in connection with the Orange Line robbery. Police said he was awaiting extradition to Chicago.

Authorities released several surveillance camera images of the suspects in the Orange Line robberies, prompting both men to flee the city.

The two allegedly boarded an Orange Line train at the Halsted stop around 4:15 p.m. on July 16, and announced a robbery after the train pulled out of the station. At least one of the men pulled out a gun and robbed several passengers, before getting off at the Roosevelt stop.

Police have said the robbers got away with about $100 in cash, an iPhone, an iPad, two laptop computers, and some credit cards. One woman was pistol-whipped when she refused to hand over her purse, but no one was shot.

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Earlier this year, police said CTA security cameras also helped lead to the arrests of 60 vandals who sprayed graffiti on CTA property in the first three months of the year.