The bomb went off just after 3:30 a.m. in the heart of Times Square. It caused little damage and no injuries, but the 2008 explosion left an enduring mystery about who set it off, and why.

The attack bore close similarities to two earlier bombings at high-profile Manhattan locations: All occurred around the same time of night, and in each case the assailant was seen biking from the scene, wearing a sweatshirt that hid his face.

There has not been a similar attack since, and for seven years, the bomber, as well as any possible accomplices, have remained at large.

But on Wednesday, the Federal Bureau of Investigation announced that progress had been made. Investigators said that “several persons of interest” had been identified in the 2008 bombing and that all three attacks were now believed to be linked.