Well, there was a weekend on 1/15 and 1/16 this year and the letter says it is referencing the "past weekend" and that checks would go out on the 20th, so it looks to be written and sent on or about Monday 1/17/11. Maybe "Sunday the 17th" was a typo and he meant Sunday the 16th? Dunno. Don't have any more info yet.
It is possible that this is the "near riot" reported late last year by the local residents.
Record requests have been made to the LCSO, so hopefully this will be clarified if it can be matched to any incident reports from the police.