grammaticality - Is this ellipsis kosher? And why?

I stumbled upon a sentence in something Christopher Hitchens wrote eons ago. But I am iffy about its grammaticality.

And many murderers have been reprieved because they were condemned for the wrong murder, quite probably just as many as have been executed for the only murder they did not in fact commit.

I am not sure the use of "as many as" here makes the sentence grammatical, because there isn't a pronoun or noun phrase following the phrase, which seems to be an ellipsis. I thought I'd write the sentence as:

And many murderers have been reprieved because they were condemned for the wrong murder ; quite probably just as many have been executed for the only murder they did not in fact commit.

or

And many murderers have been reprieved because they were condemned for the wrong murder, quite probably just as many as those that have been executed for the only murder they did not in fact commit.

Am I wrong?