Police say Sargent, 43, killed Williams and dismembered her body, scattering her remains in a weed-choked field near York Street and Sedgley Avenue.
About 150 people gathered Tuesday evening at John F. Kennedy Plaza to remember Williams, 31, of Ogontz, and decry violence against transgender women.
Some held signs that read "Our Lives Are Not Expendable," "Transphobia Kills," and "Justice for Diamond."
Police said Sargent confessed to the slaying, saying he became enraged when he discovered Williams was transgender. Williams was also known as Mark Williams.
Gloria Casarez, Mayor Nutter's liaison to the lesbian, gay, bisexual, and transgender communities, urged the LOVE Park gathering to fight any "she-tricked-me defense" the alleged killer might use.
Casarez cited the unsolved slayings of transgender women, including Kyra Kruz, who was shot to death in September.
Williams "made some choices in life that were unsavory for some people, but we loved her," Morrison said.
Friends spoke warmly of Williams, who had a diamond tattoo near her wrist, for her personality and interests.
"She was very much into music and poetry," said Christian Lovehall, 28.
Lovehall said the last time he saw Williams, she complimented him on his nose ring and asked why he got it.
He mentioned Tupac Shakur, who also had a nose ring, "and in that moment her face lit up," Lovehall said. What followed was a 30-minute conversation on hip-hop and poetry.
"She had a warm and loving spirit," Morrison said.
Contact Robert Moran at 215-854-5983 or firstname.lastname@example.org, or follow @RobertMoran215 on Twitter.