"We're going to keep the pressure on," the Chelan County Sheriff told USA TODAY June 12 as he prepared to board a helicopter to help in the search.

The girls, Olivia, Evelyn, and Paityn, were found dead near a campground on June 2, three days after they were last seen alive.

Law enforcement officials said they have tracked a subject believed to be Travis Decker, the father accused of killing his daughters.