He was last seen wearing pants shortly after the shooting. Perhaps he had clothes stashed around somewhere.
Then again, nudists remain a possibility. You can't trust people who have no need of pockets.
He returned to his apartment to get pants after the shooting. From there, he headed toward a wooded area. Because of the rain, tracking dogs couldn't follow a scent.
Police did not find guns in the apartment, but know that he had at least a handgun in his possession, so police assume that he has the gun.
Speculation time:
He's dead. He went into the woods, and, realizing that not only was this whole thing a bad idea, he just had his big, mean, gun taken away from him by an unarmed man. Feeling humiliated on top of the realization that he will be captured and probably killed, he killed himself. The police can't do a "regular" missing person/cadaver search in the woods, because they assume that they are dealing with an armed and dangerous man, so they have to be extremely cautious, and thus less efficient, in their search.
At least, that's my theory. Of course, he could be very much alive in those woods, but I can't believe he got very far. And I don't know how big the woods are. The impression I got based on news stories was something of only a square mile or so, but I really have no idea. I haven't checked any maps.