CHICAGO (CBS) — Protesters angry over the fatal police shooting of Laquan McDonald are not giving up their fight to convince Cook County State’s Attorney Anita Alvarez to resign for her handling of the case, organizing a sit-in at her Loop office on Thursday.

A group of community activists, clergy, and labor leaders converged at 69 W. Washington St. on Thursday, demanding Alvarez step down. Protesters occupied the entire lobby, shouting “Anita must go!” They also handed over a stack of petitions which they said contain more than 35,000 signatures demanding her resignation.

They said there was no excuse for it to take Alvarez 13 months to file charges against Van Dyke, when the shooting was caught on video.

Alvarez has said she won’t resign, and has defended how long it took to bring charges, saying she won’t apologize for conducting a “meticulous and thorough investigation” of the shooting. She said she will let voters decide if she should keep her job in the upcoming election, when she faces two challengers in the Democratic primary in March.

Protesters said that’s not soon enough, and no guarantee she’ll be gone.

“We the people today stand beside you and before you in solidarity, asking for Anita Alvarez to resign. Not tomorrow, not next month, not next year, but today; today she must go.,” said Alexandrea Navedo, with the Workers Center For Racial Justice.

Protesters have accused Alvarez, Mayor Rahm Emanuel , and former Police Supt. Garry McCarthy of trying to cover up the fatal shooting, by fighting to keep the video under wraps for more than a year, and not filing charges until after a judge ordered the video made public.

“There are three leaders who by failing to do their jobs have failed the residents of Chicago. Fierce community organizing has succeeded in removing one. Anita Alvarez and Rahm Emanuel are next in line. Anita must resign, Rahm must resign, and every other elected or appointed official complicit in this cover-up must go,” said Amisha Patel, with the Grassroots Collaborative.

Emanuel also has said he will not resign, although earlier this week, he dismissed McCarthy, saying the Police Department needs new leadership to help restore the public’s trust.

The protesters said they’re also demanding justice for Miguel Flores and Erick Lagunas, who were killed in a Thanksgiving Day crash with an off-duty police officer in 2007. They said it was an injustice that prosecutors dropped charges against Officer John Ardelean in 2010, even though prosecutors had obtained video showing him drinking heavily just before the crash.

At the time they dropped charges of aggravated DUI and reckless homicide, prosecutors said they had no choice. Weeks earlier, a judge had ruled Ardelean was arrested without probable cause, and tossed out evidence of the officer’s blood-alcohol content, effectively gutting the case.