Struck did the same thing he does when his own 2-year-old daughter is upset. He began to softly sing "Twinkle, Twinkle Little Star."
Somewhere in one of the lullaby's verses, a bystander snapped a photograph of Struck and the child. Her family's white SUV lies upside down in the grassy field behind the two. A paramedic is seen treating another passenger in the background.
Struck, holding the barefoot girl on his hip, points at something outside the frame. The child holds the fingers of one hand in her mouth, and clings to Struck's shoulder with the other.
That image whipped through online social networks, rendering Struck a heartfelt hero.
"I had no clue [the bystander] was right there," Struck told CNN's Brooke Baldwin on Tuesday. "It was just me and that little girl."
The photographer, Jessica Doug Matrious, had witnessed the single-vehicle roll-over crash on June 18 in Brighton, which is a suburb of Denver. She shared the image with CNN affiliate KDVR.
"He was definitely trying to keep her from watching what was going on behind her," Matrious told KDVR
. Matrious said she could see the child relax in Struck's arms.
Brighton Police said all six passengers
-- two adults and four children -- were thrown from the car during the accident.
Police said preliminary findings indicated that none of the occupants was properly restrained, but that there was no indication that alcohol or drugs were involved.
The girl's father was declared dead at the scene, according to police. The mother and all four children were transported to area hospitals.
When emergency responders were dispatched to the scene, Struck spoke first to the girl's 4-year-old brother, who wasn't responding to him. That's when a paramedic passed the girl into his arms. Realizing how close they were to the other family members -- several of whom were unresponsive -- Struck carried her from the scene, hoping to distract her.
"I took her away into the little grass field," Struck said. "And that's when all my emotions started coming to."
Struck said he immediately thought of his own daughter, also 2 years old.
"That's where I thought, oh man, this girl's the exact same size as my little girl," he said. "She's crying. She's soaked in gasoline."
And she was quite possibly experiencing the most terrifying moment of her life. Her own dad had just been killed, mere steps away. Struck said all he could think of was how he comforts his own child when she cries: He sings to her.
"My daughter will start singing halfway through," Struck said. "And she'll stop crying and kind of calm down. So I tried that with this girl, and sure enough, it worked. She stopped crying. She was just rubbing my shoulder with the beat."
He began pointing out the emergency lights and the nearby helicopters, ready to airlift several of her family members to the hospital. He kept singing, meandering through the verses. He realized the beat to "Twinkle, Twinkle Little Star" aligns precisely with the pattern of flashing lights on the firetrucks and police cars.
The Brighton Police Department shared the photo on its Facebook page
. Commenters praised Struck's actions as selfless, instinctive and heroic.
Asked how the family is doing, Struck implored people to remember the family in prayer. He said the girl from the photo and her sister were released from the hospital, but that another baby and her 4-year-old brother were still in bad shape.
"The family definitely needs many prayers," he said. "We just need to keep praying for them."