Norris was well-known for creating the giant mosaics of glass tiles. And while they look just fine from far away, police say a closer look at some of them revealed a shocking discovery -- squished in between the whimsical pictures of trees and animals, police say they found something that was not so innocent.
"Last week the city was made aware that offensive images have been embedded in some of the murals on city property," San Francisco Police Chief Greg Suhr said.
Hidden in some of the tiny glass tiles that are only an inch wide are pictures that police say carry a sexual theme.
"A negative of a photograph that is inlaid behind the clear tile itself," Cmdr. Mike Biel said. "I think as an adult, you would look at these tiles and see possibly some sort of connotation to them."
In all, police say they have found about 100 of the inappropriate tiles, spread across four different murals, including one at Sunset Elementary School.
Suhr says it is unlikely kids would have stumbled upon these tiles on their own.
"These tiles are very small; you would have to get close to these tiles to see the inappropriate images," he said. "Some of the tiles are at such a height that you wouldn't be able to see them without an apparatus."
The school district is reassuring parents.
"We don't have any evidence that children were harmed in the development of these murals," Deputy Superintendent Richard Carranzasaid.
Police say they will continue inspecting Norris's other murals one tile at a time.
"It's a big investigation to take on and no resource will be spared to take it on; the safety of our kids in San Francisco is paramount," Suhr said.
Police say they will surgically remove and photograph each offensive tile and take it into evidence.
Meanwhile, Kid Serve, the non-profit where Norris taught art skills to children, has been shut down.
If he is convicted, Norris could face up to 10 years in prison.