CANADENSIS, Pa. (AP) - Pennsylvania State Police say an unmanned balloon brought in from Ohio has not been helpful in the search for a suspect in the killing of a state trooper.

Trooper Tom Kelly, a state police spokesman, says the agency returned the Mylar balloon to the Ohio Department of Transportation on Tuesday.

Kelly says dense brush and rugged terrain in the Pocono Mountains search area hampered use of the tethered device, which is akin to a weather balloon.

The Ohio agency sent the balloon last week as troopers entered a sixth week of searching for 31-year-old Eric Frein (freen).

Kelly says it was experimental and among several technologies being used.

Frein is charged with opening fire outside the Blooming Grove barracks on Sept. 12, killing Trooper Bryon Dickson and seriously wounding Trooper Alex Douglass.