Four Chicago men were arrested last week after a seven-month undercover investigation into heroin dealing on the city’s West Side near Oak Park, according to a statement from the village Wednesday.

The investigation came to a close June 7 with the arrests of Raynell Davis, 24, Demarcus Moore, 27, Colran D. Bates, 26, and Darrell Lipscomb, 49.

Oak Park police investigators had identified three of the suspects-Davis, Moore and Bates-operating in the area. Undercover officers with the West Suburban Enhanced Drug and Gang Enforcement, or WEDGE, then made more than 15 heroin purchases ranging from two grams to 22 grams. During the series of purchases, the Cook County State’s Attorney’s investigative unit collected evidence for prosecution.

Davis, Moore and Bates were arrested June 7, and Lipscomb, who had not been previously identified, was found to be in possession of more than 100 separate foil packets containing nearly 74 grams of heroin.

All four suspects were charged with calculated criminal drug conspiracy, a Class X felony that carries a penalty of six to 30 years in prison.