The severed head of a goat was found near the corner of the building stuffed inside a pink gift bag.
... and later in the story...
She said that whomever it is has her attention and that of police.
That's a remarkable gift bag that can accommodate an entire building.
As far as the second error goes, yikes. Use whom only when it's the object of a phrase -- for whom the bell tolls; to whom she sent the goat's head. In this sentence, the sender "has her attention," and is the subject.