What was the third occasion when the Chicago PD fought supernatural opponents?

From Small Favour, chapter 17:

"We've gone up against the supernatural three times", she [Murphy] said quietly. "It's ended badly twice."

We meaning the cops, of course. I nodded.

One occasion is when the Loup Garou got loose in the police station and killed Ron Carmichael and a number of other people.

Another occasion (the one that didn't go badly) was the SI raid on Leonid Kravos, with Harry and Michael's assistance.

What was the third occasion?