Dante Dears of San Diego had already served time in prison for being a pimp. When he was released and it became clear to law enforcement that he was up to his old business again, they put him under surveillance and observed him using a smartphone consistently over the course of several hours. Police obtained a warrant to seize the phone and search the information contained on it. But they couldn’t figure out how to unlock it. So they sent it off to an FBI lab and people there couldn’t unlock it either. Now, the feds are seeking a new warrant to serve Google, compelling the company to unlock the phone for them. That application was uncovered by privacy/security researcher (and frequent MTR guest) Chris Soghoian.
From Ars Technica:

Soghoian wonders about the legality of accessing a still-operational cell phone. “Given that an unlocked smartphone will continue to receive text messages and new emails (transmitted after the device was first seized), one could reasonably argue that the government should have to obtain a wiretap order in order to unlock the phone,” he argues.