Besdies the whole "We all know who it was" thing, I don't think the Secret Service gives a damn who brought it in. They don't prosecute drug posetion crimes.
They investigated enough to find out if their security failed, or if someone went around their security. If the first, they updated protocols, if the second, they brought it up with that person's boss, and possibly updated protocols on going around security. In either case they aren't going to publicly say what part of the protocols failed, were circumvented, or were changed.
They certainly aren't going to waste time running DNA on it.