LOLO, Mont. -

Authorities have brought back their ground crews and are concentrating on roving patrols. The Missoula County Sheriff's Department is joined by U.S. Marshals, the FBI andd A.T.F. in the search of the remote area.

Orange highlites evidence areas where David Burgert allegedly fired upon sheriffs deputies and fled into the woods Sunday. The peace officers weren't injured but they did return fire.

An Army National Guard chopper, equipped with heat sensors didn't find any trace of Burgert. "We really can't pin him down to a specific drainage or mountainside or immediate area," said Missoula County Undersheriff Mike Dominick. "So we've got more outlying patrols than guys searching on the ground."

"He's reported to be a skilled woodsman," said Dominick. " The foliage there is that such with a pocketknife you could create a campsite in 15 minutes."

If Burgert is still in the area. Investigators have impounded two of his cars. They're still looking for one he was reportedly seen in three weeks ago.