Over several weeks, thieves hit about a dozen locations, including three Hammond high schools.
About a dozen thefts, mostly to light poles, have been reported. Police believe the thefts are being committed by the same group of robbers.
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The suspects were nabbed during a traffic stop at about 2 a.m. Saturday during which time they found a "large amount of copper wire."
The individuals were seen coming out of the Cook County Forest Preserve in Calumet City, police said.
The suspects' names and charges were not immediately released.
Hammond police, working with multiple other law enforcement agencies including the FBI, said "additional suspects may be identified and charged as the investigation continues.
Some of the thefts occurred in the middle of the day. Witnesses may have seen the thieves and thought they were utility workers, thus not reporting them.
Gavit High School was the first school to be targeted, resulting in the postponement of a Friday football game and cancellation of a planned alumni night. Wires were taken from Clark High School's field lights just before their Homecoming game. Thieves also hit the shuttered Hammond High School.