IIRC, something similar happened in the 1980's/90's with the phone landlines. The FBI/DEA made an anonymous toll-free tip line for people to call with tips on

IIRC, something similar happened in the 1980's/90's with the phone landlines. The FBI/DEA made an anonymous toll-free tip line for people to call with tips on the cartel activity. The cartel was able to get the phone records for people who called the tip line through bribes, extortion, or violence to the telco employees. They identified the people who called the tip lines, and then one-by-one eliminated them all.