Before taking the cash, Martinez had assured Fenerty "I don't do this for a living" - and the evidence backed him up.
Martinez used his personal e-mail account to send his demand, and discussed it openly on the phone and during a meeting in Fenerty's office. In both cases, the FBI and agents from the city Inspector General's Office were listening and recording, court files show.
Martinez, a 30-year-old unemployed father, hatched the plan after hearing a parking authority officer allegedly offer to fix tickets for a South Philadelphia shop owner in return for some bootleg DVDs.
Martinez, who said he had clashed with the same unidentified officer over tickets of his own, whipped out his cellphone and caught the exchange on video.
Then Martinez fired an e-mail to Linda Miller, deputy director for the parking authority.
"I have footage of one of ur PPA officers buying bootleg movies and ppa officer saying give me two movies and I will remove ur tickets for free with no problem," he wrote from his gmail account, according to his plea memo. "Contact me before I go public."
Miller passed the information to Fenerty, her boss, and thus began a two-day dance with Martinez. Officials first appealed to his sense of citizenship, and asked him to surrender the video so they could investigate.
But Martinez told Fenerty "being a good citizen wouldn't put food on his family's table," according to the memo that Assistant U.S. Attorney Anthony Wzorek read to the judge.
Martinez also said at least two local news outlets had offered to pay him for the video. "I can stall but not for long," said one of his e-mails. "I am very upset about this and people of Philadelphia WOULD BE TO."
When Fenerty told him the authority can't pay for evidence, Martinez ramped up his requests. He warned that a TV station was "hounding" him for the footage.
The next evening, Sept. 14, 20111, Martinez brought the video and his laptop to Fenerty's office. He played the tape for the director, predicting it would get 150,000 hits an hour on YouTube.
With his office wired, Fenerty repeated that it would be illegal for the parking authority to pay for evidence, but offered to give Martinez something out of his own pocket to protect the agency's reputation. They negotiated, and Martinez accepted $500. Then he handed over the tape and agreed to delete it from his computer.
At his plea hearing, Martinez confessed that he didn't realize at the time he was committing extortion but understands it now.
"I know I did something wrong and I have to fess up to what I did wrong," Martinez told the judge.
He seemed eager to elaborate after the hearing, but his lawyer, Federal Public Defender Mark Wilson, urged Martinez not to comment until his sentencing.
Wilson explained that Martinez thought he was exposing a corrupt officer and that he might get a reward for it. "He wanted to be a whistle-blower," the defense lawyer said.
What became of the video - and the officer in it - is unclear. Martinez said that officer is no longer writing tickets in his neighborhood.
Linda Miller, the department's deputy director, said she could not discuss the case because it involved "an ongoing investigation."
Wzorek, the prosecutor, said only that no other arrests have been made.
"Our city officials are not for sale," Inspector General Amy L. Kurland said in a statement. "Those who try to extort or bribe them will be held accountable."
Contact John P. Martin at 215-854-4774, at firstname.lastname@example.org or follow @JPMartinInky on Twitter.