In Garner's Modern American Usage, Garner provides the following quote from a newspaper article:
“There are a number of people who might have wanted to kill Robert [...], but the intervening two decades have failed to reveal whom [read who].”
and follows it with this analysis:
Although whom might seem to be the object of reveal, in fact the relative pronoun is the subject of an implied verb--failed to reveal who [might have wanted to kill Robert].
Why exactly can't whom be used here, similarly to any personal pronoun, as in ...reveal them / him or her (or them) ?
Secondly, could a nominative personal pronoun be used with a similar elliptical reasoning? E.g., ...reveal they [who might have wanted to kill Robert]