In DC, brick-throwing is against the law, as are rioting and disorderly conduct. The guy who drops off the bricks hasn't done any of those things. Doing things that might result in a law violation is not a crime. Conspiracy to throw bricks is a crime, but this is not a conspiracy; it is not an attempt, nor is it a threat to damage property. There is nothing in DC law that criminalizes this action. It could be a federal crime to damage government property, so the brick thrower can be prosecuted. Under 18 USC 2
(a) Whoever commits an offense against the United States or aids,
abets, counsels, commands, induces or procures its commission, is
punishable as a principal.
(b) Whoever willfully causes an act to be done which if directly
performed by him or another would be an offense against the United
States, is punishable as a principal.
Aiding and abetting is explained here (archived version, dunno if anything has changed).
That the accused had specific intent to facilitate the commission of a crime by another;
That the accused had the requisite intent of the underlying substantive offense;
That the accused assisted or participated in the commission of the underlying substantive offense; and
That someone committed the underlying offense.
A reasonable person could find that the underlying offense had been committed (throwing is not itself a crime, so I'll say that there was property damage); Larry's actions did assist in the commission of the crime; and Larry had the intent required (this is distinct from Curly, who was supposed to deliver a load of bricks to a construction site, and had the wrong address).