Nearly three months since Travis Decker allegedly murdered his three daughters, officials are attempting to be "abundantly thorough" in combing through the areas near the crime scene, with the FBI closing several roads, trails and campgrounds in Leavenworth, Washington -- including the site where Decker's three children were found dead.

       "We will not relent. We will not give up," Chelan County Sheriff Mike Morrison said during a press conference on Monday. "The girls would not want us to give up."

       In an order posted over the weekend, the U.S. Forest Service said "all of" the Rock Island Campground, along with two other campgrounds, will be closed to "allow the FBI to conduct an ongoing investigation."

       While there has not been a "break in the case," over 100 FBI personnel are on the ground searching a quarter-mile radius around the crime scene to collect "all possible evidence" on where the fugitive father might be, according to Peter Orth, supervisory senior resident agent for the FBI Seattle field office.

       Authorities said on Monday they have no evidence that Decker is either alive or dead. Morrison believes if Decker is alive, he must be "pretty tired by now."

       "He's got to be perfect every single day; we just have to be perfect once," Morrison said.

       The search area overlaps with where Decker's truck and the three girls' bodies were found back in June.

       Paityn Decker, 9; Evelyn Decker, 8; and Olivia Decker, 5, were found dead near the Rock Island Campground in Chelan County, Washington, on June 2, after they left home for a planned visit with their father on May 30, according to police.

       The closure began on Sunday morning and will be in effect until Wednesday at approximately 6 a.m., according to the forest service. A list of several roads, trail heads will also be closed off to the public, officials said. But, officials told reporters on Monday that the closure may continue, possibly through the end of the week, if detectives need more time.

       "We want to bring closure. We want to bring answers," Morrison said on Monday.

       The search -- which officials said had been in the works for more than several weeks -- will allow for investigators to pass along sufficient information to other authorities as the search "could take years."

       "If it's not me wearing this uniform, it's another Chelan County Sheriff. We will find him, in one fashion or another," Morrison said.

       Everyone will be prohibited from entering the closed areas except "any federal, state or local officer or member of an organized rescue or fire-fighting force" or anyone with a U.S. Forest Service permit allowing access to "roads, trails or areas restricted by regulation order," the forest service said.

       The closure of this campground comes one week after the Chelan County Sheriff's Office released disturbing new details about the crime scene and the DNA evidence that they say indicates Decker, a 32-year-old Army veteran, is the sole suspect.

       The U.S. Marshals Service is still offering a reward of up to $20,000 for information leading directly to Decker's arrest.

       Officials said anyone who sees Decker or knows of his whereabouts should call 911 immediately and not contact or approach him. He is currently wanted for three counts of first-degree murder and three counts of kidnapping, officials said.

       Decker is considered armed and dangerous, officials said.