Other times, in those moments of father-son revelry, the two would hold each other and Jesse would confide: "We're best friends and best buddies!"
Every Father's Day, the two would attend a car show in a neighboring town. They'd gawk at Model Ts and Studebakers and grab an ice cream cone from a restored Good Humor truck. "Happy Daddy's Day," Jesse would say.
Father and son were working to restore a 1948 Ford tractor. Jesse's plan was to have it ready for the Newtown Labor Day parade and throw candy from the back.
At the tender age of 6, Jesse had become interested in politics during the November election. He couldn't pronounce the president's name: "Rock Bomber" is what he would say. The two planned a trip to the nation's capital for spring so Jesse could learn more about the nation's history.
On December 13, Jesse's mind was far from that trip to Washington. He was thinking of the gingerbread houses he was to make with his class the next day. Father and son stopped at the Big Y grocery store before they headed home.
In the newsstand section, Jesse flipped through a gun magazine. That wasn't unusual. His father was a former marksman and taught Jesse how to shoot a BB gun, always standing over him and showing him proper shooting techniques.
Searching the pages, Jesse stopped on one bearing images of three guns: a Glock handgun, a Sig Sauer handgun and a .223-caliber Bushmaster. The next day, Adam Lanza entered Sandy Hook armed with all three.
Jesse asked his father about the guns. Heslin told him that Americans use the weapons for protection and carry the handguns in holsters. He told Jesse about the military-style rifle on the page, too.
"They use them in the Army to kill with," Jesse said.
"Yeah, pretty much, Jess," Heslin responded.
Dad didn't think much about it at the time, but after the shooting he returned to the magazine rack and flipped to the page to "make sure what I remembered was true." Heslin later told that story to lawmakers in Washington as he campaigned for gun control.
Heslin points to the side of his head and then his forehead, indicating the two bullets that struck Jesse. "His fatal shot was to his forehead and it exited the back of his head," he says. "Clearly he was standing face to face with Adam Lanza and clearly looked him in the face."
Ten of Jesse's classmates survived; Jesse's last word, his father was told, was "Run!"
"I can't say it brings me comfort," Heslin says.
The dad's monotone slows to almost a grunt: "I hope Jesse's words did help save those children."
"I accept what happened. I don't like it. I can't change it. Of course, I wish it never happened. I wish I wasn't part of it," he says.
"I think more so than anything I'm just disgusted. I'm disgusted that I lost my little boy, disgusted that something like this happened, disgusted it could happen; disappointed that we as a society let something like this happen.
"I ask myself: 'Why?'"
Killer's house still standing
What pushed Adam Lanza, 20, to the extreme may never be known, but clues lie somewhere behind the plywood that covers the front door of the spacious yellow colonial at 36 Yogananda Street.
It's difficult to get a good glimpse of the home from the road because it sits so high on a hill on two acres of land. The home was last appraised at $523,620 in 2012. Dozens of similarly nice homes worth well over half a million dollars dot the neighborhood.
With scenic views of the rolling hills of southern Connecticut, it's not where you would expect to find a boy who would become one of the nation's most notorious killers.
It was in that home where authorities found more than 1,600 rounds of ammunition, at least 10 knives, three samurai swords and a slew of other weaponry.
His mother, Nancy Lanza, was found shot through her forehead by a .22-caliber rifle left in her second-floor bedroom. Nearby was a blue-and-white duffel bag containing 50 rounds of rifle ammo, ear protection, eye protection, binoculars, paper targets and a certificate from the National Rifle Association bearing Adam Lanza's name.
A gun safe and smashed computer equipment were discovered in the basement where Adam lived. Books found inside the home included two related to autism -- "Look Me In The Eye" and "Born On a Blue Day" -- as well as one related to guns, "NRA Guide to the Basics of Pistol Shooting."