Updated 02/02/12 – 2:32 p.m.

CHICAGO (CBS) — In what her office is calling a “shift in philosophy,” Cook County State’s Attorney Anita Alvarez has announced the formation of a new unit that will actively review criminal cases involving questionable or wrongful convictions.

“My job’s not just about racking up convictions, it’s about always seeking justice; even if that measure of justice means that we must acknowledge mistakes of the past,” Alvarez said in a speech to the City Club of Chicago at a luncheon on Thursday. “My office is demonstrating our commitment, and our duty to bring our very best efforts to ensure that only guilty people are convicted here in Cook County.”

Alvarez said the new 6-person “conviction integrity unit” will look into criminal cases in which questions about the integrity of convictions have been raised.

LISTEN: WBBM Newsradio’s Mike Krauser reports

“Based on what we’ve been dealing with in these last couple of years, and also because of DNA and the fact that 30 years ago we could not do what we do today … we should be able to work up these cases and look at these cases and reevaluate them,” Alvarez said.

The unit will provide a more proactive approach to re-investigating cases where there might have been a wrongful conviction, according to the state’s attorney’s office.

Alvarez said it’s not unusual for prosecutors to, in effect, investigate their own prosecutions.

Aside from DNA evidence, Alvarez said police investigations have changed and include videotaping of interrogations in murder cases.

“We’re going to be looking at, number one, you know, particularly in cases where you have confessions; you can’t just have a statement, you must look at what other evidence corroborates what that offender is stating,” Alvarez said. “We’re looking at that, looking at DNA and the ability to work up pieces of evidence that 30 years ago could not be worked up.”

She said the state’s attorney’s office has about 35 cases that are getting a closer look.

The Center on Wrongful Convictions at Northwestern University said that, in Cook County, there have been 25 documented cases involving false confessions that led to wrongful convictions.