For four months in 2018, authorities in Texas collected more than 9.2 million messages under a single court-authorized wiretap order, newly released figures show.

The wiretap, granted by a federal judge in the Southern District of Texas, was granted as part of a narcotics investigation and became the federal wiretap with the most intercepts in 2018, according to the government’s annual wiretap report.

Little is known about the case, except that 149 individuals involved in the case were targeted by the wiretap. The wiretap expired last year, allowing the judiciary to disclose the case.

To date, no arrests have been made

Trailing behind it was another narcotics investigation in the Eastern District of Pennsylvania saw police obtain a three-month wiretap that collected 9.1 million text message from 45 individuals. No arrests were made either.

The two cases represent the largest wiretap cases seen in years.

Wiretaps are some of the most invasive kinds of lawful surveillance in the hands of U.S. prosecutors outside of the federal intelligence community. Where pen registers and trap-and-trace devices allow authorities to see when a call is placed and to whom, wiretaps grant police real-time access to phone conversations and text messages. Given the privacy-invasive nature of real-time listening capabilities, the bar to obtain a court-ordered wiretap is far higher than other surveillance measures.

But the overall number of wiretaps authorized and subsequent convictions “fell sharply” in 2018, the U.S. Courts said in its annual transparency report.

A total of 2,937 wiretaps were authorized in 2018, down 22% on the year prior. The report also said that number of wiretaps using encryption went up, rendering the wiretap ineffective.