Investigators for the FBI have scoured hundreds of hours of video and interviewed more than 900 people so far in the pipe-bomb case. They’re reportedly studying the way the person walks in the camera footage, hoping to find a suspect match through gait analysis. But they’ve made little progress, and they’re asking members of the public for help. “We’re still nose to the grindstone here and trying to find this individual, trying to bring the person to justice,” Steven D’Antuono, the assistant director of the FBI’s D.C. field office, told the Associated Press this week. “But there is hopefully maybe somebody still out there that knows the person or sees the video again.”

In many cases involving homemade bombs, investigators can identify an attacker by tracing where the bomb’s pieces were purchased or acquired. But sometimes there aren’t many clues. “When I look at the news reports of this pipe bomber, [authorities] are focused on the gait of the individual. That tells me that they don’t have a lot of info on the bomb itself and how it was constructed,” says Lis Wiehl, a former prosecutor and the author of Hunting the Unabomber: The FBI, Ted Kaczynski, and the Capture of America’s Most Notorious Domestic Terrorist. A year might sound like a long time for a manhunt. But when “the bomb itself doesn’t give them the clues they need, a year is not that much,” Wiehl told me.