(CNN) With the glide of a paint roller, Manuel Oliver silently released a loud call to action -- "We demand a change."

His son Joaquin "Guac" Oliver was one of the 17 victims slain in the Marjory Stoneman Douglas shooting . Like Joaquin's classmates, Oliver is determined to make sure no more families suffer the same tragedy.

"He didn't say anything, he was just breathing heavily while painting. He was very focused," Lex Michael, a Parkland survivor who captured the emotional moment, told CNN. "It's not shown in the video but Oliver also took a hammer and created holes in the wall and put flowers in them."

The father then invited students to sign their names and write notes of support on the mural.

The event is part of "Parkland 17," an art exhibit organized by Miami Heat player Dwyane Wade and created by artist Evan Pestaina in Wynwood, Miami. It also includes empty desks with students' names and a phone booth where visitors can "Call Your Rep" to talk about gun control, according to Michael.

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