This sentence: Ashcroft announced his intentions to the media Sunday after stark criticism, and withheld from revealing anything else for the rest of the conference.
is poorly constructed.
1) The verbs do not match. A compound sentences (or a sentence with a compound predicate) calls for two sentences joined by "and" (or another conjunction) but their structure (in good writing) must be parallel.
2) The use of withheld is incorrect:
Ordinarily, withheld is an action verb used like this: We withheld information from the audience. One withholds something from someone. A person does not withhold from doing something.
And not: We withheld from informing the audience. The only possible reading I can come up with is that the author meant to say: And he held back on revealing etc. That could be used but why use it if it provides no additional semantic meaning?
Better would have been:
Ashcroft announced his intentions to the media Sunday after stark criticism and revealed nothing else for the rest of the conference.
That is a simpler construction and parallel. And obviously, in a parallel construction, there would be no comma as may be seen in the reference given below.
For those who like references, here is a link to parallel construction
Comma usage can be complicated but in a well-constructed parallel compound sentence (or a sentence with a compound predicate), there simply is no need for one. Indeed, it's really one of the simplest notions without any ambiguity or complexity.
Note: This is not a compound sentence entirely. It's one sentence with a compound predicate.
The girls sang songs and made jokes all night. No commas.