Street said he was "seriously considering supporting" Williams but decided the state senator "would be a disaster for the black community." He took issue with the $5 million the founders of Susquehanna International Group invested in Williams' 2010 run for governor because of his positions on education. Williams ran for governor that year on a pro-school-voucher platform.
Williams yesterday called Street a "longtime family friend" but didn't want to comment about his Facebook claims.
"I respect him for his legacy," Williams said. "I don't have much else to say."
Street, brother of former Mayor John Street, could have a more interesting impact on the 2015 race than when he ran in 2011.
And that could be very good news for City Controller Alan Butkovitz, another Democrat expected to run for mayor next year.
Street, who is African-American, did better in the five predominantly black wards in North Philly in 2011 than he did in other parts of the city. He could draw votes there from Williams, also an African-American, and benefit Butkovitz, who is white.
Gaming the racial math is a common tactic in city politics.
Former City Councilman Frank Rizzo, who is white, switched his registration from Republican to Democrat in November and says he also might run for mayor.
Rizzo, tight now with political allies of Williams, could sap white votes from Butkovitz.
Street, who raised very little money for his 2011 race, said he hasn't spoken with any elected or Democratic Party officials in the city about his plans.
"Why should I talk to them to be rejected?" Street asked. "I've been to prison. I owed taxes."
Street spent 26 months in federal prison and then a halfway house for three misdemeanor counts of not paying taxes on $3 million in income from 2002 to 2004. Philadelphia and New Jersey also have claims against him for unpaid taxes. In all, he owed $1,141,741 in back taxes, according to the claims filed against him.
Street says he is still paying the court-ordered $100 per month toward his original $413,704 federal tax bill. He said he has not paid anything to Philadelphia or New Jersey for those tax claims.
On Twitter: @ChrisBrennanDN