The 27-year-old officer received a call about a fight happening outside a Target in Ansonia, Connecticut, on Monday, but when he arrived, he saw a group of young neighborhood kids just hanging out, he told ABC News.
Castillo, who has been an officer for three years, then noticed that one of the boy's bikes was broken, so he grabbed some tools out of his SUV cruiser and set to work, fixing the bike chain and tightening up the tire.
"I told them, 'All right, guys, go play somewhere else besides the Target parking lot,' " Castillo told the news outlet. "They're good kids."
Little did he know that Faith Taylor, a passerby, had snapped a photo of the sweet moment and posted it to the Ansonia Police Department Facebook Page.
"…it's nice to see an officer in a good and kind way… Give this guy some kudos!" she wrote.
The photo has received almost 1,000 likes and over 300 shares since it was posted on Monday.
"It feels great. It really does," Castillo told News 8. "There is so much negativity in police work everywhere, just to get this one thing, it's so small to me, I was just helping a kid out, but it's big to everybody else. I think this shows a positive outlook on police work."