Crews were working to clean the mural on Scoville Avenue just south of Lake Street Wednesday morning.
"To see it vandalized, defaced this way, it's shameful," said Oak Park Area Arts Council Executive Director Camille Wilson White.
Parts of the mural was painted over in order to make it read "All Lives Matter."
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"If they cannot understand that all lives don't matter until Black lives matter, they did this out of hatred," said activist and mural organizer Cortlyn Kelly.
About 20 volunteers painted the mural over two days in June with bright, inclusive and symbolic colors.
It was made to be more colorful than other BLM murals around the country. Organizers said they intended that distinction to reflect Oak Park's diversity and to be as inclusive as possible since this mural was going up during Pride month.
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Oak Park resident Cullen Benson approached the Oak Park Area Arts Council with the idea in the wake of protests after George Floyd was killed.
"This is a piece of history to influence generations to come," Benson said last month.
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On Wednesday, some who live nearby shared their reactions with ABC7.
"The village is a place of inclusion and to have someone come and destroy someone else's work is disrespectful and disgusting," said resident Yolanda Taylor.
Resident Greg Mayor said, "If all lives matter then Black lives matter, and why would that upset you other than if you have a different agenda other than all lives matter?"
Kelly hopes the incident serves "as a wake-up call."
"Use this as another conversation starter," Kelly said. "When we starting this mural, we wanted people to have conversations and clearly more conversation needs to be had."
By Wednesday night, the mural has become even more colorful than when it was first painted. Supporters added chalk writings and drawings to echo the larger message.
The Revolutionary Oak Park Youth Action League organized a demonstration Wednesday night, continuing calls to defund and pull police officers from schools.
"If you were brave enough to home out here and cover this up, you should be brave enough to come be a man and just tell us what you did," said Ray Longstreet.
The group's message to those who vandalized artists' and activists' work is that hate has no home here.
'Black Lives Matter is not just a movement," said mural designer Franka Huanchicay. "It's not just a political statement, but it is just about people."
"If you hear Black Lives Matter and immediately your response is to say 'All Lives Matter,' says a lot about how you perceive race," said Makayla Pye, of the Revolutionary Oak Park Youth Action League.
Oak Park police are investigating the incident.