" Gunmen clad in Iraqi National Police uniforms kidnapped between 100 and 150 people at a government research institute in Baghdad Tuesday in what may be the** largest ever mass kidnapping** in the war-torn city. "
Should this read, " in what may be the largest mass kidnapping ever" ??
I know the grammar experts around here will know far more about this than I do, but my instict is to say that the word “largest” modifies “ever” and belongs where it is in the original sentence. The way you’ve rewritten it results in the modifier being misplaced.
I do too. When I’m editing, I eschew all unnecessary hyphens. My occamy rule of thumb is: When in doubt leave it out. I only insert a hyphen if its absence causes confusion. So in the example question, I’d leave it out. It would not, of course, be incorrect to insert it, but the sense of the sentence is perfectly clear without it; only an exercise in grammatical minutiae would absolutely require it.
They might have been imprisoned in the same place they were kidnapped…
Back to the OP, I think the way it was written is correct, but the way Cartooniverse has suggested it is written is fine too - it’s perfectly readable.