(CNN) -- It happened in just seconds, by all accounts.
A pistol in the hands of a 4-year-old boy went off Saturday, killing Josephine Fanning, the 48-year-old wife of Wilson County Sheriff's Deputy Daniel Fanning.
The tragedy has shaken the town of Lebanon, Tennessee, a community just east of Nashville beside itself with grief.
Days after the Tennessee shooting, the intersection between children and guns emerged again, this time in Toms River, New Jersey.
A 4-year-old boy shot another boy, age 6, in the head with a .22-caliber rifle Monday night. They were playing in a yard, police said. The boy is alive, in stable condition at a hospital.
As the gunplay persists, lawmakers in Washington wrestled this week with the divisive politics of firearms.
In Tennessee, the woman died during what had been a lazy, happy day at a home cookout.
Deputy Fanning and a relative went into a bedroom to look at some of the lawman's guns, said Tennessee Bureau of Investigation spokeswoman Kristin Helm.
Later, Josephine Fanning and the boy -- who was the deputy's 4-year-old nephew -- walked into the room.
At some point, the boy picked up a loaded pistol from a bed, Helm said. It was the deputy's personal weapon, not his service pistol, she said.
With a single shot, Fanning's wife was dead.
The deputy and Josephine had been married only about a year.
In an unusual move, Deputy Fanning told his story in an e-mail he sent to CNN affiliate WKRN.
He wrote that he had set down his off-duty weapon "only seconds before the tragedy."
"I would like the viewers to know that officers of Wilson County do not make a habit of leaving loaded guns simply lying around," he wrote.
"The door to the room the accident happened in stays locked unless we were sleeping or we were in it," Fanning wrote. "This was the only loaded gun in the house other than my duty weapon, which was locked away."
Wilson County Sheriff Robert Bryan said Fanning had been showing "another person that was there at the house some of his weapons he had locked in a secure gun safe," reported CNN affiliate WTVF.
No one saw the boy enter the room, WTVF quoted Bryan as saying.
"Split second," Bryan said. "We're talking about seconds for that kid to walk in that room unbeknownst to them, grab that gun and it goes off."
"He took all the precautions, he's a trained law enforcement officer, trains with weapons all the time."
Deputy Fanning also works as a school resource officer at Lebanon's Sam Houston Elementary, reported CNN affiliate WSMV.
The state bureau said it has taken all witness statements and its initial investigation is complete, but the bureau's case will remain open until the final autopsy and evidence is analyzed in the crime lab, Helm said.
No charges have been filed, said the Tennessee Bureau of Investigation, which looks into incidents involving law enforcement officers.
"Nobody is immune to this," Bryan told WSMV. "It doesn't matter if you are a law enforcement officer. These things can happen in seconds."
CNN's Julia Talanova, Matt Smith and Joe Sutton contributed to this report.