Marketplace Tech Podcast (June 2020)
Discusses the 2015 demonstrations in Baltimore to protest the death of Freddie Gray. Many people were arrested on completely unrelated charges because they were in the vicinity of the protests based on cell phone records.
Chicago police acknowledge they have had cell-phone interceptor devices since 2008. Also notable, the FBI requires state and local police to keep quiet about the capabilities of the surveillance gear.
New York Times (February 2016)
New York police used covert cellphone tracking devices on at least 1,000 cases between 2008 and 2016. This was unknown to the public previously as the FBI maintains it is "necessary to ensure that criminals and terrorists do not learn to circumvent the devices".