Cops are investigating a campsite found in the Washington state woods where Travis Decker is believed to have gone on the run after allegedly killing his three young daughters -- this according to Chelan County Sheriff Mike Morrison.

Police tracked a subject believed to be Travis Decker, 39, after a weeklong manhunt. Decker is accused of killing his three daughters — Paityn, 9, Evelyn, 8 and Olivia, 5 — whose bodies were found at a Washington campsite on June 2.

A search for Decker has been underway since the bodies of his three young daughters were found at a campground near Leavenworth on June 2.