Former San Marino, California, mayor Dennis Kneier is seen on this surveillance video throwing a bag of dog poop onto Philip Lao's walkway. (ABC News)

By JAMES WANG, RICHARD BRENNER and ALEXA VALIENTE

The former San Marino, California, mayor who resigned after admitting to tossing a bag of dog poop on a neighbor's sidewalk says it was a "mistake."

"I was tired in the time that I did it," Dennis Kneier told ABC News' "20/20."

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Kneier's neighbor, Philip Lao, went to police after he found a plastic bag of dog feces on his sidewalk on June 7. After checking his home surveillance video tape that monitors the exterior of his residence, Lao identified Kneier to police as the man who threw the plastic bag on his walkway.

"I admit, you know, when I saw the video and I thought, 'Hey, since he can do this, I can too,'" Lao told "20/20." "But my wife talked me out of it."

Philip Lao put this "No Poop Zone" sign in front of his San Marino, California home. (ABC News)

While Kneier was mayor, Lao fought against Kneier's proposals to paint bike lanes along the road and adding lights to the tennis court.

"We have disagreements in terms of he comes to the city council, and he objects to things," Kneier said.

Kneier apologized and resigned as mayor, but Lao and others now want him off of the San Marino City Council.

"I don't know what else I can do. I can't turn back to June the 7," said Kneier.

ABC News' Nick Watt contributed to this report.