On Tuesday the Federal Communications Commission (FCC) Chairman Ajit Pai disclosed in a letter that the agency has reviewed over 50,000 documents as part of its investigation into the sale of real-time phone location data by carriers. Pai also said the FCC has nearly completed its investigation.

Motherboard previously revealed that T-Mobile, Sprint, and AT&T had been selling real-time location data to middlemen companies for years, which then provided it to bounty hunters and other third parties. Motherboard demonstrated the power of the data by paying a bounty hunter $300 to track a T-Mobile phone in January. Verizon also sold data to a similar company.

"The FCC's Enforcement Bureau has been working actively on this important investigation," the letter from Pai, addressed to Chairman Doyle of the Committee on Energy and Commerce, Subcommittee on Communications and Technology, reads. The letter was entered into the record during an FCC oversight hearing Thursday.

"For example, the Bureau's staff to date has reviewed over 50,000 pages of documents that were submitted in response to Letters of Inquiry and Supplemental Letters of Inquiry issued by the Bureau," the letter added. These are letters that the FCC sends to telecos to request information.

Do you know anything else about this investigation? We'd love to hear from you. Using a non-work phone or computer, you can contact Joseph Cox securely on Signal on +44 20 8133 5190, Wickr on josephcox, OTR chat on jfcox@jabber.ccc.de, or email joseph.cox@vice.com.

The FCC's investigation has been far from speedy, however. A source familiar with the FCC investigatory process previously told Motherboard that this particular investigation could have moved quicker, and that the FCC Chairman's office, when it wants, can act faster. FCC Commissioners have also said that the agency has withheld information about the investigation from them, and members of Congress were concerned that the FCC would not investigate the sale of phone location data before the one year statute of limitations runs out.

After Motherboard's initial investigation, 15 senators called on the FCC and the Federal Trade Commission (FTC) to investigate.

Pai added that the investigation may be complete soon.

"Based on the latest update I have received, the Bureau's investigation is nearing its conclusion, and I am confident that the Bureau will be able to announce the results no later than the end of January. I will provide you with those results as soon as practicable," Pai's letter added.