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Gregory Graniss, suspected of vandalism during World Series victory celebration. (San Francisco Police Department)

A former San Marin High School athlete accused of smashing a Muni bus windshield after the Giants won the World Series pleaded not guilty to two charges Monday -- though his attorney said he is ashamed of his actions and takes responsibility for what he did.

Gregory Graniss, 22, appeared in San Francisco Superior Court to plead not guilty to felony vandalism and tampering with a passenger vehicle with intent to cause great bodily injury. He was arrested last week after a photo of him swinging a street barricade toward the window of a Muni bus drew wide attention on Facebook and Twitter.

The incident occurred early Oct. 29 during the celebrations after the Giants swept the Detroit Tigers to win the World Series.

"He is very, very sorry," said Douglas Rappaport, Graniss's attorney. "He wants to set a good example and show he is willing to stand up and take responsibility."

Graniss, who is free on $40,000 bail, showed up with his parents for the San Francisco court appearance and said little.

The reason for the not-guilty plea, Rappaport said, is that "he had no intent whatsoever to injure anyone, and that's why he is pleading not guilty to the second charge," which includes the phrase "intent to cause great bodily injury."

"There's a difference between trying to hurt someone and being exuberant during a celebration," Rappaport said. As to the first charge, "we'll sort out whether he's responsible for a felony or misdemeanor vandalism. The difference is you could end up behind bars for up to three years for one or on the other hand get a whole heck of a lot of community service for the other."

During his senior season at San Marin in 2007-08, Graniss was a key member of the basketball team that helped turn the program around and helped it qualify for the postseason.

"He was born and raised in Novato. Both of his parents went to high school in Novato. Obviously, he's wrong here. Everybody makes a mistake once in his life and his just happened to get caught on camera," Rappaport said.

San Francisco District Attorney George Gascon held a news conference after the arraignment and said he hopes Graniss' arrest will not be the only one in connection with the bus vandalism, Bay City News reported.

Others were caught on camera during the Oct. 29 riots, including a man smashing the Muni bus and two people who set it on fire.

Graniss' next court date is Dec. 17, Rappaport said.

Contact Janis Mara via email at jmara@marinij.com. Follow her at Twitter.com/jmara.