– The FBI is still being thwarted by an encrypted phone in the San Bernardino terrorist shooting investigation. "We still have one of those killers' phones that we haven’t been able to open," FBI Director James Comey told the Senate Intelligence Committee Tuesday, per the Los Angeles Times. "It has been two months now and we are still working on it." That's making it difficult for investigators to track communication between Syed Rizwan Farook and his wife Tashfeen Malik before they were killed in a police shootout after the Dec. 2 attack. The FBI said last month it was having trouble cracking encryption on multiple phones and hard drives in the case. It's not clear whose phone is still causing trouble. Comey said law enforcement is sometimes unable to unlock phones even after obtaining warrants ordering the phones be opened, the AP reports. The FBI is trying to retrace the couple's movements before and after the attack—last month, investigators said they couldn't account for an 18-minute stretch after the attack—and determine whether anyone else helped. At this time, the FBI still has no evidence the couple had "outside direction or support," the Times notes, but other questions remain: Investigators don't know whether the couple planned other attacks, whether anyone knew about the plans for the Dec. 2 attack, or why Farook left a bag containing homemade pipe bombs in the conference room they attacked. The FBI's encryption struggle illustrates what law enforcement has been warning about for more than a year—advanced encryption methods on some newer phones often hinder investigations, particularly at the state and local levels.