The Devil's Night existed long before the film was made or even the graphic novel. According to wikipedia it had been going on since the 1940s, it started with mischievous and petty criminal acts and escalated to arson in the 70s, getting progressively worse until the 90s. How much influence the film had on the massive destruction caused in 1994 is, probably, impossible to say.

There was a marked increase in 94.

I'm not trying to be confrontational, but this is what wikipedia says about Devil's night: "The destruction reached a peak in the mid- to late-1980s, with more than 800 fires set in 1984, and 500 to 800 fires in the three days and nights before Halloween in a typical year. By the early 1990s, Detroit saw little decline in Devil's Night arson. After a brutal Devil's Night in 1994, then-mayor Dennis Archer promised city residents arson would not be tolerated." According to this, the peak was in the 80s but it kept pretty much the same in the early 90s, with 1994 standing out due to a particularly brutal night. I'm just trying to understand if what happened in 1994 was a natural escalation of a situation that had been bad for about a decade or if there's any sort of evidence that the movie was indeed responsible for it.