Authorities said the white smoke seen shortly after one of the detonations indicates small bombs with a simple, low-velocity, explosive mixture -- not military grade.
"[The attackers] may not have the resources as we have seen in other bomb attacks, but they knew how to make the bomb go BOOM," said Nick Casale, security expert and former NYPD officer.
Experts also pointed to large pieces of metal, seen flying through the air in one of the videos, which suggests the bomb may have been concealed in a mail box or trash barrel. However police said today there's no hard evidence they were hidden in trash cans.
The limited damage to nearby buildings told experts the bomb may have failed to fully function as designed. If it did somehow malfunction, former NYPD bomb squad member Kevin Barry said Boston was potentially saved from "much more catastrophic injury and possibly more death."
ABC News' Lee Ferran, Angela M. Hill, Cindy Galli and Matthew Mosk contributed to this report.