I didn't ask how many were killed, I asked how many there were. How many district attorneys were there along that I-80 corridor between Youngstown and New York between 1996 and 2005? A few dozen? Lots of rural counties, lots of guys like Gricar that get re-elected or run unopposed and hold the seat for years. Can't be too many. And out of those three dozen or so, one had an attempt made on his life, and another went missing.
You cite the statistics of murder of prosecutors as a reason to deem it unlikely. Well, what are the statistics for prosecutors that just vanish without a trace? How many times has that happened in the last 100 years? Once? Twice? Ten times? Way less than murder or attempted murder.