BOSTON — Gail Jones says she has forgiven the man who shot and killed her 23-year-old son during a botched robbery at a New Hampshire Army surplus store five years ago.

But she is hoping her son’s death, in which a stolen gun was used, will prompt gun owners to be more careful about locking up their firearms.

Jones is suing the grandfather of the man who killed her son and two other men, alleging that his failure to secure his gun properly enabled his grandson to steal it and use it in the shootings on July 2, 2007.

Michael Woodbury is serving a life sentence in the deaths of Gary Jones, of Halifax, Mass., William Jones, 25, of Walpole, Mass., and James Walker, 34, of Denmark, Maine. He admitted to killing the men.

Walker was the manager of the Army Barracks store, a military surplus and outdoor gear store in Conway, N.H. Gary Jones and William Jones were friends who happened to stop by on their way home from a camping trip in Maine. Woodbury said he killed the men when they tried to tackle him during the robbery.

Jones said she hopes her lawsuit will send a message to gun owners to make sure their guns are stored securely.

“That is where I’ve taken this, not out of retaliation because it’s not that,” she said. Instead, her hope is that “maybe something else can become of it, and in this instance, just maybe trying to stiffen up the gun laws in New Hampshire or putting some responsibility on a homeowner that owns guns.”

Jones faces an uphill battle. A federal judge in New Hampshire dismissed the lawsuit last year after finding that Jones had not proven her claims that Woodbury’s grandfather, Lawrence Secord, was negligent.

Jones appealed to the 1st U.S. Circuit Court of Appeals in Boston, which heard arguments in the case June 5. The court is expected to rule within the next few months.

Woodbury, 31, of Windham, Maine, had been released from prison two months before the shootings after completing a five-year sentence on robbery charges. In the weeks leading up to the shootings, Woodbury went on a multi-state crime spree that included robbing a bank in Florence, S.C., holding up a clothing store in Chattanooga, Tenn., and breaking into a home in St. Simons Island, Ga., and then setting it on fire.

Authorities said he stole the .22-caliber handgun from his grandfather’s hunting camp in Wentworth Location, N.H., a family camp he had visited while growing up.

Jones claims in her lawsuit that Secord should have taken steps to secure his gun when he learned his grandson had returned to the area after being released from prison. She also says he failed to report the theft of the gun promptly.

But U.S. District Judge Paul Barbadoro found that Secord was not negligent because the door to his camp was locked, and Woodbury broke a window and entered without Secord’s permission. The gun was unloaded and hidden under a hot water heater platform. The judge also found that Secord did not learn about the burglary or gun theft until after the killings.

The judge also noted that the New Hampshire Supreme Court has recognized that people cannot be held liable for the criminal acts of third parties.

Secord’s lawyer, Anthony Campo, said Secord kept the gun in a locked hunting cabin. He said Secord had only seen his grandson once briefly in the 12 years before the shootings.

“It’s obviously a tragic event and nobody is downplaying that, but with regard to the law, it’s a non-starter,” Campo said.

New Hampshire has a law that holds people liable if a child gains access to a gun and uses it in a reckless or threatening manner or during a crime, but does not have a law requiring guns to have trigger locks or to be locked in secure containers.

“The law is what’s reasonable under the circumstances,” Campo said. “It was in a locked hunting cabin and it was secured.”

Jones’ lawyer, Roberto Tepichin, said Woodbury had seen his grandfather briefly about a month before the shootings, and that Secord should have known Woodbury might try to steal the gun.

“His grandson was familiar with the gun, he had used it growing up, he was familiar with the cabin, he knew there was a hidden key and he could have pushed the door open to get in, given his history of breaking and entering, and bank robbery,” Tepichin said. “In that situation, it’s like dangling meat in front of a lion, so to speak.”

Gary Jones was a plumber’s apprentice who loved BMX biking, traveling and hiking. His mother said her lawsuit is not aimed at getting vengeance against Secord.

“What we’re trying to do in New Hampshire is to just get the word out there that if you are a gun owner, you need to be responsible, you need to take precautions.”