A Jacksonville, Florida, community is mourning the loss of two heroes. Scott Wulff, 61, and his dog Astrid were killed when both were struck by an Amtrak train last Sunday. Witnesses say Astrid, apparently spooked by the oncoming locomotive’s lights and sounds, broke loose and ran toward the track. A panicked Wulff followed, trying desperately to capture Astrid and pull her to safety.

“I heard the train speeding by, then a loud breaking sound,” Isaiah Boone told PEOPLE. “So, I go outside and I see everybody drop down on the ground in tears. When I heard what had happened, I immediately told my restaurant I had to go, had to get away from the scene and walk.”

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Boone works as a cashier at Wok & Roll, located just across the street from the accident scene, where Scott and Astrid were regulars, even when money was tight.

Image zoom Jacob Wulff

“No matter how much or how little he had, he would always feed his dog first,” Boone said, noting that the pair were popular among vendors and visitors in the Murray Hill neighborhood, lined with independent shops and cafes. “He made sure he let everybody know how much he loved her and how proud he was of her. She was his world.”

“Anywhere my dad went, Astrid was there,” Scott’s son, Jacob told PEOPLE. “She was his best friend.”

And with good reason. Scott rescued Astrid, a Staffordshire Bull Terrier, from the streets in 2013.

“She was homeless and running loose on a bad side of town,” Jacob said. “She ran straight to him and he just fell in love.”

Image zoom Jacob Wulff

A paw injury and severe malnourishment suggested Astrid had been on the run for weeks and Scott suspected that she had been neglected and possibly tossed from a vehicle. When a weeks-long search for the dog’s owners turned up nothing, “she just became his,” Jacob recalled.

And he became hers.

“My dad struggled with depression and alcoholism throughout his life,” Jacob said, noting that in recent years, his father had become sober, held down a landscaping job, mended family relationships and loved spending time with his granddaughters, five-year-old Audrey and 1-year-old Lauren. He credits Astrid with much of his father’s recovery and joy in his final years.

Image zoom Jacob Wulff

“She was his accountability partner. She depended on him for her survival and he knew that so having her really helped him keep his act clean. It was almost like his second shot at parenthood – taking care of someone. That was their relationship. Astrid helped my dad get through a lot of his depression and face his personal demons.”

News of Scott’s and Astrid’s deaths hit hard for both the Wulff family and the Jacksonville community.

Image zoom Jacob Wulff

“My heart sank,” Jacob says of hearing the news from a Jacksonville Sheriff’s Office deputy. “I remember feeling numb and dropping to my knees.”

Fighting tears, Jacob told PEOPLE that he hopes sharing Scott and Astrid’s heartbreaking story will move others.

“People may say, ‘It’s just a dog.’ But for someone to literally stare death in the eyes for something they believe in or someone they love is so incredibly selfless. One thing I’ve learned from my father in recent years is that people need to value life a lot more, and not just our own lives. We need to value others’ lives, too. He did that for Astrid, but what about all the homeless pets who don’t have anyone to put their lives on the line for them? I’ve never been more proud of my father than I am now.”