CHICAGO (CBS) — Just five days until Chicagoans choose their next mayor.

But on Thursday, Toni Preckwinkle launched a new ad attacking how Lori Lightfoot investigated a critical failure of the 911 call center.

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CBS 2 political reporter Derrick Blakley is taking a close look at the claims.

The new ad is based on a very real tragedy: A 2004 West Side fire that killed three of Dwayne and Emily Funches’ children, as well as a 12-year-old godson.

In a CBS 2 report, neighbors said their calls to 911 weren’t taken seriously. Lori Lightfoot was then chief of staff at OEMC and her leadership was criticized by a Cook County judge, after the city lost most of the 911 tapes critical to the investigation.

“And her response, according to a judge in the case, was lax, cavalier and covering up,” Preckwinkle said.

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“I specifically directed the staff to make sure those tapes were preserved. Unfortunately, they were not but that had nothing to do with the deaths of those children,” Lightfoot said.

Preckwinkle insisted it’s fair to recount the incident 15 years later, because it casts doubt on Lightfoot’s integrity and ability to lead.

“You don’t engage in cover-ups when things go wrong. You take responsibility and try to address the problems,” Preckwinkle said.

But Lightfoot dismissed the ad as act of desperation for a campaign that’s failing.

“The notion that you’re going to try to score political points in a tragedy in which four children died is really, I think, a new all-time low,” Lightfoot said.

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CBS 2 tried to contact the Funches family and even went to their West Side home in an effort to get their opinion on use of the fire tragedy in a campaign ad. CBS 2 did not reach them.