Minneapolis, Minnesota - A series of photos posted to social media by a colleague show workers at Minneapolis VA Medical Center, where Alex Pretti worked, holding a tearful moment of silence in his honor.

"A moment of silence for Alex Pretti. One of our colleagues!! May he rest in peace," Pretti's colleague Garrett Peterson wrote on Facebook, alongside a series of pictures showing Intensive Care Unit staff lined up in silence.

The attached images show dozens of ICU staff visibly crying, some with their heads in their hands, while they honor their slain coworker.

Pretti, an ICU nurse who worked predominantly with veterans, was fatally shot by Customs and Border Protection agents on Saturday while exercising his legally protected right to observe law enforcement.

Video released since the shooting shows CBP agents violently piling on top of Pretti and beating him before an agent steps back and opens fire.

Pretti's parents referred to him as a "kindhearted soul who cared deeply for his family and friends and also the American veterans whom he cared for" – a sentiment shared by his friends and colleagues.

Dr. Aasma Shaukat, who hired Pretti in 2014, told CNN that he was "all about being a good citizen, standing up for your neighbors, your community, and standing up for what he believed was unjust or unfair."

"It was complete disbelief and utter shock," Shaukat said of the moment she realized that it was Pretti who had been killed. "I couldn't believe that this was our Alex, the Alex we knew."