The day before he died, Jesse Lewis, 6, etched a brief, sweet note in the frost on his mom's car door. "I love you," it read simply in remarkably neat first-grade handwriting.
It was the last note she'd ever receive from him, Scarlett Lewis tearfully tells PEOPLE – and thankfully, she caught it on film.
"I said, 'Oh, Jess, I have to take a picture of that,' " she says. "Thank God."
This week, PEOPLE tells Jesse's heartbreaking story and remembers the other lives lost in one of the worst school shootings in U.S. history.
Twenty students and six faculty members lost their lives in the massacre on Dec. 14. Among the victims were principal Dawn Hochsprung, who lunged at shooter Adam Lanza, first-grade teacher Victoria Soto, who tried to hide her kids in a closet, and four other brave Sandy Hook Elementary School employees who strained desperately to save the children they loved.
Soto died, her cousin Jim Wiltsie tells PEOPLE, "a hero."
Thanks to her quick thinking, some of her students were able to flee. But many others – including Jesse – didn't survive.
Tenacious and strong, like Hochsprung, Jesse also tried to rush the shooter (who also killed his mother, Nancy Lanza, 52, earlier that day), and in doing so, died.
In emotional interviews, his parents tried to put to words a grief beyond compare.
"Jesse had no fear and thought he could conquer the world," says his father Neil Heslin, 50. "He was a brave little boy who had no fear – and he always put everybody before himself."