Ah, it's making sense now. Thanks Cindy.
The back wall of the cemetery abuts some brownstones and is about 100 feet from the notorious E 3rd Street clubhouse of the Hell's Angels motorcyle gang. According to "Hell's Angels: Three Can Keep a Secret if Two are Dead" by Yves Lavigne, the biker gang stockpiled C-4 in the 1980s and one Manhattan member roams the nation teaching other gang members how to use explosives.
Looks like the detail about the note was put into the article as part of the ongoing anti-Christian agitprop campaign by partisan media shills.