The Boston Marathon bombers used July 4th fireworks to make their bombs.
Accused mastermind Tamerlan Tsarnaev came to a fireworks store in New Hampshire, an hour's drive from Boston, in February.
The staff remembers him well and were horrified when they learned of their unintended role in the terrorist attack.
According to Phantom Fireworks store manager April Walton, the suspect was only interested in the most powerful fireworks.
"I was shocked, it was very unsettling to know that he had been here in the store. He asked what was our loudest and most powerful firework in the store."
He paid $200 for a mortar shell kit and even got a second for free in a two-for-one deal. The box was marked "lock and load" and "barely legal."
INSIDE EDITION's Megan Alexander asked, "Tell me what you can about this."
Walton said, "It is a reloadable kit with 24 shells, it comes in packs of six. Each pack of six has their own watch tube for safety reasons, and you take the shell and open one fuse and drop it in. Ignite it, and it shoots up in the air and does a colorful loud display."
INSIDE EDITION obtained the receipt of Tamerlan's purchase.
Alexander asked, "Does it give you chills to see this?"
Walton replied, "Absolutely, it is frightening to think he was here in the store."
At a safe location, INSIDE EDITION detonated the fireworks identical to the ones Tamerlan bought.
But how did the bombers create a destructive weapon from fireworks?
Investigators believe they opened up the canisters and used the gunpowder inside to improvise the bomb.
Nicholas Casale, a counter-terrorism expert said, "When you take that simple black powder and compress it, whether in a pressure cooker or pipe, as a pipe bomb, it is going to increase it's level of explosion. It is going to be deadly."
There is growing outrage today over revelations that Tamerlan was living on welfare, even as he was plotting to bomb the marathon.
“What Nerve!” said the headline on Wednesday’s Boston Herald.
State officials confirm that Tamerlan and his wife Katherine, a convert to Islam, received welfare payments until 2012 when Katherine’s income made them ineligible.
The mournful strains of "Taps," played during the funeral of Sean Collier, the MIT police officer that was shot and killed in a shootout with the terrorists. Vice President Joe Biden attended the funeral.