Officials overnight narrowed the manhunt for Travis Decker, the Washington state father suspected of killing his three daughters, to a small, rural area inside the county where the girls were last reportedly seen alive.

Flanked by local and state law enforcement, U.S. Marshals were looking for the 32-year-old Army veteran near the small unincorporated community of Peshastin and the Ingalls Creek and Valley High areas, a spokesperson for the Chelan County Sheriff's Office confirmed to USA TODAY Tuesday morning, June 10.

Peshastin is about 20 miles east of Rock Island Campground. where the bodies of Decker's school-age daughters were found slain on June 2.

Late Monday night, the sheriff's office issued an alert announcing law enforcement increased its presence, concentrating search efforts in those areas, where "he is believed to potentially be." The search area is near Blewett Pass and the Wenatchee Mountains.

"Please secure your homes and vehicles, stay alert, and report any suspicious activity to 911," the sheriff's office, the lead agency on the triple murder case wrote in the alert, warning people they "will see a visible increase in law enforcement presence tonight as a precaution.... If you see something say something."