No one will be charged in the death of a 7-year-old boy who shot himself with a handgun stashed with a toy in the family's Plymouth home while other children played nearby, authorities said Tuesday.

Despite a long-running and extensive investigation and with a specific suspect in mind, Police Chief Mike Goldstein said, law enforcement failed to establish who was responsible for the gun at the time Keyaris Samuels shot himself in the head on a weekday afternoon in May 2018 at Common­Bond Communities' Vicksburg Commons, a townhouse complex on N. Shenandoah Lane.

The inability to sufficiently connect the weapon left in a box with a new hoverboard to a suspect — either through fingerprints, DNA or other evidence — led to the decisions by the Hennepin County Attorney's Office and the Plymouth city attorney to decline filing charges.

The now-inactive case could, however, be reopened if any new information becomes available, the chief said.

"Keyaris Samuels, a young, innocent victim, should not have died because of the reckless and irresponsible actions of an individual who left a loaded, unsecured handgun in a residence where four young children resided," Goldstein said, adding that prosecutors had no choice but decline to charge anyone.

"No family should ever have to endure such a senseless tragedy."

Goldstein said police have a "good idea what happened," referring to a family friend who was arrested four days later as being the one who likely put the loaded gun where children could find it.

"But you can't bring a good idea into court and have it hold up in a court of law," he said. "As frustrated and as angry as I am, we can only act on what we have in front of us."

Soon after the first-grader's death, the chief vowed that "we will do everything in our power to hold the gun owner or owners accountable for their irresponsible and unconscionable actions."

The investigation spanning more than a year included several interviews, the collection and examination of DNA and other evidence by his department and the state Bureau of Criminal Apprehension, as well as phone analyses by a specially trained Plymouth police officer and later by a private company, a move that Goldstein said is rare and meant added expense for his department.

Fifteen months later, Goldstein was left to express pride in "the work done by our officers and investigators during this yearlong investigation. No stone was left unturned."

The County Attorney's Office said in a statement Tuesday that "we support the thoughtful statement made by Chief Goldstein and don't have anything to add at this time."

Goldstein said his officers notified the boy's mother, Kyuandria Samuels, Tuesday morning about the investigation coming up short. He said she "reluctantly understands."

Melissa Coleman, Keyaris' grandmother, said Tuesday that "I've put it in God's hands" to mete out justice. In the meantime, she said on behalf of her family, "We cry all the time, we think about it all the time, but we celebrate the 7 years of his life."

A court document filed soon after the shooting revealed that the gun may have been left there by the family friend who was arrested four days later.

Keyaris' mother arrived home shortly after the shooting and told police she was unaware the gun was in the box and that it was not hers. She tied the gun to her friend, who had failed to show up for a meeting with his parole officer earlier in the day of the shooting in connection with a felony drunken-driving conviction.

The friend, the chief said Tuesday, declined to cooperate with the investigation.

Goldstein said police did determine who originally bought the gun, but "it since has changed hands many times, and I don't mean in an illegal way."

The chief said that the lack of any legal requirement for each time a firearm has a new owner added to the difficulty of finding the person who was responsible for the gun when Keyaris shot himself.

"It would certainly be helpful" to have some record whenever a firearm changes ownership, Goldstein said. "How it would get done, I don't know. … But with the proliferation of weapons that are out there, they are not hard to get ahold of."