The FBI, trying to figure out whether anyone else was involved in the plot, thought that Farook's county government-issued cellphone might have the answer. In February, the bureau announced that its technicians were unable to get into the iPhone, which they feared had been set up with a security feature by Farook that would permanently destroy encrypted data after 10 unsuccessful login attempts.

Source: Los Angeles Times March 27, 2018 20:37 UTC