Friday, federal agents raided the Tarzana home of Albert Abrams, 63, the president of the Los Angeles Board of Neighborhood Commissioners. FBI agents confiscated a computer and records.
The raid was one of dozens conducted in a child pornography investigation.
It wasn't known who downloaded the child porn and nobody has been charged.
Abrams led a group that acts as a liaison between the many city neighborhoods and City Hall. Abrams has served on the board since 2008. The position is unpaid.
Mayor Antonio Villaraigosa's office received a phone call from Abrams over the weekend and a resignation letter.
The mayor says he hasn't personally spoken to Abrams.
In a Los Angeles Times report, Abrams blamed his behavior on a tumor that was removed recently from his spine. A medical condition he told the Times "caused behaviors that were completely out of character."
The mayor says he's appalled that anybody would engage in the type of behavior alleged against Abrams.
"The behavior is abhorrent," said Villaraigosa. "I don't know enough about his condition to comment on that."
According to the FBI affidavit, agents had probable cause there would be child pornography on the computer. Now they have to prove that it was Abrams who downloaded it to his computer before he can be charged.