https://www.techdirt.com/articles/20211212/08511448107/massachusetts-supreme-court-tackles-law-enforcement-use-cell-tower-dumps.shtml

Years after they've become a go-to tool for law enforcement to work their way backwards to suspects, the Massachusetts Supreme Court is wrestling with the issue of cell tower dumps.

Cell tower dumps can often be had with only a subpoena. They give investigators access to all cell phones that were in the area of the tower at certain times. Investigators peruse these lists of numbers to try to find numbers that might be linked to someone who committed a crime. The problem is investigators don't know who that "someone" is, so they, however briefly, turn everyone in the area into a suspect.