Some people wanted to, but the police failed to reveal they

Question

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]

Answer 1

(For simplicity, I'm interpreting the intention of "who might have wanted to kill Robert" to mean Robert's killer, but this choice doesn't affect the analysis.)

In "...decades have failed to reveal [the killer]", "the killer" is the direct object of the transitive verb "reveal". Anything that replaces "the killer" will also be a direct object, so it makes sense naively that "whom" would be correct since it too comes after "reveal".

In "...decades have failed to reveal [who might have wanted to kill Robert]", the phrase in brackets is a noun phrase and the entire direct object. "Who" is clearly the subject of the noun clause, so in this sentence, "who" is correct.

Now, in the original sentence, if "whom" was meant only as a pronoun to replace "the killer", then "them" or "him or her" would have been good choices, but not "who". The original analysis is correct, and "who" is the right choice, though, for what it's worth, many native speakers make this mistake, and few would notice it.