Call it a mayoral race mystery.

Just how did former State Sen. T. Milton Street Sr. come to sign the nomination petition for former City Councilman James F. Kenney last week?

Both are candidates for the Democratic nomination for mayor in the May 19 primary.

Brian Villa, a Democratic committeeman from West Philadelphia's 27th Ward, said he attended a "petition party" last week at Ladder 15, a Center City bar. There, Villa said, he circulated nomination petitions for Kenney's mayoral campaign, Helen Gym's bid for City Council at-large, and Carol Jenkins' bid for the Board of City Commissioners.

Street happily and knowingly signed all three, Villa said.

A picture of Kenney's petition, provided by Villa, shows the candidate's name in bold at the top of the page. Street's signature is on the fifth line.

Candidates for mayor need the signatures of at least 1,000 registered voters from their political party. Voters can sign only one petition for mayor.

Street was cryptic about why he signed Kenney's petition.

"Signatures on a petition mean nothing more than a person's ability to be on the ballot," he wrote in an e-mail. "That is the beauty of this process."

Street left it to his son, T. Milton Jr., to explain further.

Street the younger blamed it all on confusion and a dimly lit bar.

"My father would have never signed Jim Kenney's petition," said Street, the field coordinator for his father's campaign. "It was in the spirit of the moment. Everyone was passing around petitions, and we were signing."

Villa counters that he was sitting at a well-lit booth in the bar and told Street exactly which candidates he was signing for.

"He was fully informed, and he knowingly and voluntarily signed," Villa said. "I specifically asked Milton Street if he would sign Jim Kenney's petition."

Kenney declared for mayor on Feb. 4. Street has said he will formally announce his campaign Thursday.