Philadelphia (CNN) It was a botched robbery that led to Philadelphia police officer Sgt. Robert Wilson's death in 2015.

Wilson had just stopped in to pick up a video game for his son's excellent report card when he ran into two men attempting to burglarize the video store.

Suddenly, the men opened fire on him, said fellow cop Jonny Castro.

"He drew their fire away from the customers, basically, saving their lives," Castro said.

Wilson's heroic efforts set in motion a new journey for Castro.

Now he's a forensic composite artist for the Philadelphia Police Department.

And Castro uses his artistic ability to honor law enforcement officers, firefighters and military servicemembers killed in the line of duty.

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"On the one year anniversary of [Wilson's] death, I spoke with his sister and asked her if she would mind if I painted a portrait of him," recalled Castro.

"He was promoted to sergeant at his funeral, so he never had any photos in a sergeant's uniform. So, I've painted him wearing his dress uniform with sergeant stripes and with his medals on -- medal of honor and medal of valor. His family loved it."

Wilson's portrait became Castro's first work of art paying tribute to fallen heroes across the country. Now on portrait of valor number 107, he finds it a challenge to keep up with the number of police deaths in the line of duty.

"I can't do every single officer. Right now, I'm behind ... but even when I start working on one, I'll get the notification that another was killed somewhere else."

Art student to Army vet

Castro's love of art and sketching started at an early age because of his father's influence.

"My dad was a big artist, he taught me a lot," Castro said.

After beginning art school, 9/11 happened and Castro felt compelled to join the Army.

"I decided to finish out my freshman year. My dad was a Vietnam veteran. He served two of the worst years over there, and he told me a lot of stories about it and I wanted to experience that," recalled Castro.

He spent nearly a year serving in Iraq before he returned home and joined the Philadelphia Police Department.

Castro uses a virtual paintbrush and a digital tablet and spends roughly 8-10 hours on each portrait. He does this in his spare time off from his policing job in the graphic arts unit. Since he began his self-funded art project, Castro paints two portraits a week.

Castro creates his portraits with a virtual paintbrush and a digital tablet.

He researches the fallen officer before rendering a blot that aims to capture each story of bravery in every image. Once finished, Castro contacts the fallen officer's department and shares a signed copy, often framed, with the department and the officer's family.

Photos: Portraits of fallen heroes Massachusetts Institute of Technology police officer Sean Collier was shot and killed by the Boston bombing suspects in 2013. This digital portrait of Collier is one of many created by Philadelphia police Officer Jonny Castro as a way of honoring first responders and military personnel for their sacrifices. Click through the gallery to see more of Castro's portraits. Hide Caption 1 of 11 Photos: Portraits of fallen heroes San Antonio Officer Miguel Moreno was shot and killed last June in Texas while investigating a vehicle break-in. Hide Caption 2 of 11 Photos: Portraits of fallen heroes Delaware State Police Cpl. Stephen Ballard was shot to death last April after stopping a suspect at a convenience store. Hide Caption 3 of 11 Photos: Portraits of fallen heroes North Carolina Department of Public Safety corrections Sgt. Meggan Callahan was beaten to death by a prison inmate last April. Hide Caption 4 of 11 Photos: Portraits of fallen heroes Lt. Debra Clayton of the Orlando Police Department was shot and killed last January in Florida after attempting to stop a murder suspect. Hide Caption 5 of 11 Photos: Portraits of fallen heroes Staff Sgt. James D. McNaughton of the US Army, 306th Military Police Battalion was shot and killed by an enemy sniper in Iraq in 2005. Hide Caption 6 of 11 Photos: Portraits of fallen heroes New Orleans Officer Marcus McNeil was fatally shot last October while on patrol. Hide Caption 7 of 11 Photos: Portraits of fallen heroes Florida Highway Patrol Master Sgt. William Bishop was hit by a vehicle while investigating a traffic accident last June. Hide Caption 8 of 11 Photos: Portraits of fallen heroes K-9 police dog Roscoe of Crowley, Louisiana, police was shot and killed while attempting to assist in the arrest of a murder suspect last March. Hide Caption 9 of 11 Photos: Portraits of fallen heroes Police Constable Keith Palmer of the Metropolitan Police Service was stabbed to death while defending London's Palace of Westminster during a terrorist attack last March. Hide Caption 10 of 11 Photos: Portraits of fallen heroes New York City Fire Department Chaplain Mychal Judge was killed in the September 11 terror attacks. Hide Caption 11 of 11

This important step in his process, Castro said, is "just so they know, they have other officers all the way across the country that feel for them. My main goal was just to make sure they get something that they can physically hold on to, and something they can hang up in their house."

Memorializing the fallen

Castro incorporates unique touches in each portrait to help capture those who made the ultimate sacrifice. He wants each image to portray who that person was -- explaining one image where the officer is split in half -- wearing his US Marine Corps dress uniform on one half and his police uniform on the other half.

"I don't want every portrait to be the same, so if they're a veteran of Iraq or Afghanistan, [the painting will include a] service ribbon, or if they were a Marine, I'll put the globe and anchor [Marine insignia] somewhere in there -- just something to give it its own personality to each painting."

In addition to fallen officers, Castro has expanded his tributes to include innocent bystanders, such as Robert Godwin Sr. The 74-year-old Ohio grandfather was gunned down on Easter Sunday earlier this year. He was killed by a stranger.

'Wall Of Heroes'

Always starting with their eyes, Castro sometimes gets emotional during the artistic process.

"I've done officers where their child was born a couple months after they were killed," he said. "Once you start hearing things like that, it starts to get a little emotional. In the end, the main goal is to make sure that child will have this painting to hang up in their room somewhere."

Jonny Castro's "Wall of Heroes"

Castro has set up a "Wall of Heroes" in his unit's office displaying 3 x 5 prints of each portrait. His work is also shared on Facebook and Twitter . But his artistic expression doesn't end there. Castro's creativity is not only displayed throughout his office -- which is covered in his favorite movie posters and action figures -- but his body is covered in similar art as well.

Castro shows no sign of stopping. His mission is to honor and remember these heroes.

"I mean they died, basically, so everyone else can live," he said. "Most of these times, these officers are killed trying to save another person. Or if they're killed just protecting -- doing stuff that they do every day. So, I would like them to know that I'm grateful for them and their sacrifice."