PHILADELPHIA (CNN) - A police officer who normally uses his talents to catch criminals is going the extra mile for the families of comrades killed in the line of duty.
Officer Johnny Castro helps give them closure by creating artistic portraits of those who were lost.
In a crammed, creative space in the basement of the Philadelphia Police Department, he stays busy with one of the oldest forms of crime-solving: forensic art.
A year and a half ago, the patrolman took on this new, more solemn duty - using a digital paint brush and tablet on his spare time to capture an officer's bravery.
"I've done a K9 officer from Louisiana, a police officer from Europe," Castro said.
He likes to include honors that some officers didn't get a chance to wear.
"He was posthumously promoted to a sergeant so he never had any photos as a sergeant. So I did him in a sergeant's uniform," Castro said.
That kind of attention to detail can go a long way for the loved ones of an officer.
"The main thing I'm concerned about is just making sure I'm drawing this person the way people that knew him," he said.
Castro's 104th sketch goes go to the family of Joel Davis, a New York State trooper who was killed in the line of duty in July.
"I want to make sure that if his son or daughter sees it, they're seeing their father," Castro said.
After Trooper Davis' portraits have been trimmed, signed and shipped, a copy will be added to the "wall of heroes" Castro's personal memorial that continues to grow.
"Even when I start working on one, you'll see the notification that another one was killed somewhere else," he said.
Keeping up has been the real challenge. He sketches two or three officers a week.
"Unfortunately, there's always going to be an officer to do," Castro said.
Before entering the police academy, Castro served in the Army as a military police officer in Iraq in 2004 and 2005.
Castro was a patrol officer for nine years before he transferred to the Philadelphia Police Department's graphic arts unit.
He said when there's no video or photographic clues in a case, his pencil and paper are a detective's last resort. His job is to draw what a crime witness or victim can recall.
"I have always been good at drawing. My dad taught me a lot with portrait work," Castro said.
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