A gunshot detection system that has cost Chicago tens of millions of dollars and is touted as a critical component of the police department’s effort to combat gun violence rarely produces evidence of gun-related crime in the city, Chicago’s nonpartisan watchdog agency concluded. In a scathing report released Tuesday, the Office of Inspector General’s Public Safety section said the police department data it examined “does not support a conclusion that ShotSpotter is an effective tool in developing evidence of gun-related …