"An inquisitive two-year-old boy reached into the purse, unzipped the compartment, found the gun and shot his mother in the head," her father-in-law Terry Rutledge told The Washington Post.
"It's a terrible, terrible incident."
He added that his son, the victim's husband, now is grappling with how to break the news to the youngster, the couple's only child.
"He has a two-year-old boy right now who doesn't know where his mom is and he'll have to explain why his mom isn't coming home," Rutledge said.
"And then, later on (in) his life, as he questions it more, he'll again have to explain what happened, so we'll have to relive this several times over."
- Nuclear scientist -
Veronica Rutledge was a scientist at the Idaho National Laboratory, a federal nuclear research facility in the east of the state, and co-authored a number of published papers.
Staff at the laboratory are "deeply saddened" by her death, a spokeswoman told AFP.
Rutledge and her husband -- who married in 2009 -- shared a keen interest in guns, spending time at shooting ranges and going out hunting.
Rutledge illustrated her Facebook page with a smiling profile photo of herself and her little boy, alongside a panoramic photo of a rainbow.
Some 30,000 deaths a year in the United States involve firearms. The majority are suicides; many others are murders. But some involve children laying their hands on loaded weapons.
In 2011 alone, 140 children and teenagers died as a result of an unintentional shooting, more often than not inside a home, according to a study from the Brady Center to Prevent Gun Violence.
Several thousand more sustained non-fatal injuries.
- Handbags for guns -
Walmart closed its Hayden location -- normally open 24 hours a day -- after Tuesday's shooting, which occurred in the electronics department. It reopened Wednesday.
Coincidentally, the retail chain is the biggest gun retailer in the United States, which has seen an uptick in gun-buying in recent years among women looking for greater personal protection.
Fifteen percent of American women own a gun, according to a Gallup poll analysis.
There has been a corresponding boom in fashionable handbags specially designed to hold a concealed weapon, including one brand called Gun Tote'n Mamas.
Gun dealer Robin Ball, speaking to local TV station KREM, expressed surprise that a two-year-old would have the finger strength required to pull a trigger.
She speculated that the absence of an external safety mechanism -- common for many contemporary handguns -- might have been a factor.
"Murphy's law just came into play today in so many ways and there are irreversible consequences for that," Ball said.
Largely rural Idaho has one of the highest gun ownership rates in the United States, as well as a rate of violent crime below the national average.
And earlier this year, its state legislature passed a law intended to pre-empt the introduction of any new federal gun control laws.
"Accidents like this cause us all to pause and remember that firearm safety is one of those areas where we can never forget the awesome responsibility that comes with gun ownership and must always be aware and living the rules of firearm safety," said Carrie Lightfoot of The Well Armed Woman, a website for female gun owners.
- Little chance for new laws -
Prospects for tougher gun control laws, however, remain thin.
In the wake of the Newtown, Connecticut school massacre in December 2012 in which 20 children died, President Barack Obama pushed for universal background checks for all gun-buyers.
But the proposal dramatically collapsed in the face of opposition in Congress, as did a bid to outlaw military-style assault rifles.
Meanwhile, over the years, a growing number of US states have adopted laws allowing their residents to obtain concealed carry permits.
In December 2011, the US Government Accountability Office estimated there were about eight million concealed handgun permits, but by June 2014, the number had grown to well over 11.1 million.
Florida has issued the most concealed carry permits -- 1.28 million. The state with the highest percentage of residents with such permits is South Dakota at 12 percent.
In August, a nine-year-old girl learning to fire an Uzi submachine gun accidentally killed her instructor at the Arizona Last Stop gun range in the southwestern state.
She was unable to control the weapon's recoil as she fired it, and an errant bullet struck her 39-year-old instructor in the head, killing him, a police report said.