Pittsburgh police have arrested a juvenile believed to have viciously attacked a Pittsburgh Public Schools teacher as they passed each other in a Downtown alley in an unprovoked and disgusting  assault that was captured on surveillance video.

"The mayor is appalled at this vicious and senseless attack," Joanna Doven, spokeswoman for Mayor Luke Ravenstahl, said Tuesday. "It appears to be a random act but this juvenile has a track record, already has, for example, a probation officer."

Just as disturbing as the assault -- in which the assailant went out of his way to approach Mr. Addlespurger before decking him with a single sucker punch to the face -- is the way that the group nonchalantly strolled away, seemingly without a care, amid smiles and casual looks back.

"We don't know the mind state that that young man was in but there's something very terrifying about it," said Pittsburgh Councilman R. Daniel Lavelle, whose district includes Downtown. "In the video it appears he was laughing afterwards, which is very disturbing."