It will forever be remembered as a dark day for the city. But the day will also be remembered for the heroic actions that saved victims.

"As Captain Bob 'Sarge' Haley said, 'Everybody ran the right way that day.' Meaning everybody ran towards where people needed help, where the bombs went off," Rich Serino, former chief of Boston EMS, told Under the Radar. "And that, I think, is what people were trained to do. And people made a difference and saved lives."

Still, the impact of the explosion was felt far beyond the blast radius.

From safety procedures to police surveillance, certain elements of the city will never be the same. And questions about the attack remain.

"Who built the bombs? A fundamental question, right? Who built the bombs?" said Bruce Gellerman, former senior correspondent for WBUR. "[The federal prosecutor] said that the bombs were too sophisticated for the Tsarnaevs to have made. They had to have resources they didn't have, they must've had help ... they don't know who made the bombs. To this day they don't know."

Ten years later, we are reflecting on this horrific event to understand the full impact of the bombing, how the city has healed, and what scars remain.

Bruce Gellerman, former senior correspondent for WBUR

Rich Serino, Distinguished Senior Fellow at the Harvard T.H. Chan School of Public Health, former Deputy Administrator for the Federal Emergency Management Agency (FEMA), and former Chief of Boston EMS