Three years ago, when Pakistani American Faisal Shahzad tried to blow up a car bomb in New York’s Times Square, he used a detonator with firecrackers he purchased from a store called Phantom Fireworks. His bomb failed to detonate, but Phantom executives went on alert to ensure they kept careful records on future customers.

So when the FBI released the names Friday of the suspected Boston Marathon bombers, William Weimer, the company’s vice president, searched through sales records to see whether the brothers had ever visited any of the company’s 1,200 locations.

Sure enough, Weimer found evidence that Tamerlan Tsarnaev, the older of the two brothers suspected in the bombings, purchased two large pyrotechnic devices, called Lock and Load reloadable mortar kits, on Feb. 6 at Phantom’s store in Seabrook, N.H., about an hour from Boston.

“Our business is a patriotic business, and our products are used to celebrate independence and freedom,” Weimer said in a telephone interview Tuesday from the company’s offices in Youngstown, Ohio. “To even think that any of our products would be used for the opposite purpose is totally offensive to us.”

Weimer said he contacted the company’s security director, a former FBI special agent, who called the FBI in Boston.

See the names and stories of the Boston Marathon victims

Tsarnaev had paid $199.99 in cash for one kit and received the other free because of a deal the store offers, Weimer said. Each kit has four tubes and 24 shells, Weimer said. The purchase was first reported on the Web site of the Wall Street Journal.

Tsarnaev had to swipe his driver’s license, which duplicated the information on a sales form. The store also has a surveillance video, but Weimer said it had been recorded over before the bombings.

Tsarnaev, 26, was killed in a shootout with police Friday, but court documents filed in connection with charges against his brother, Dzhokhar, 19, said that a “large pyrotechnic” was found in the younger man’s college dorm room.

Law enforcement officials have not officially revealed the explosives used in the Boston bombings. Some federal officials have said the explosives may have relied on black or smokeless powder. A hobbyist can buy as much as 50 pounds of black powder.

Weimer said he does not believe the amount of powder in the fireworks would have been enough to create the explosions at the Boston Marathon. “My guess is that they experimented with the powder in the fireworks to see if they could use it but probably came to the conclusion that they needed something bigger,” Weimer said.