A survivalist from Washington state has been evading law enforcement for almost a week, following accusations of killing his three young daughters. The children were discovered at a Chelan County campground on Monday, their wrists bound and with plastic bags over their heads.

Travis Caleb Decker, 32, lacked legal custody of the daughters, and it is suspected they died from asphyxiation. Decker has a military background and a deep passion for the outdoors, as stated by officials.

“We’ve received further information indicating he might have attended Mountain Survival School,” Chelan County Sheriff Mike Morrison informed reporters on Wednesday. “Additionally, we are aware he has been an enthusiast of the outdoors since childhood.”

He said the U.S. Marshals and the FBI are assisting with the manhunt.

From left, a composite of undated family photos showing 9-year-old Paityn, 8-year-old Evelyn and 5-year-old Olivia Decker. All three were reported missing Monday after their father failed to return them to their mother’s custody. Now he is wanted in connection with their murders. (Courtesy of the Wenatchee Police Department)

It is unknown if he is armed, but authorities say he should be considered dangerous.

The Chelan County Sheriff’s Office is advising anyone who sees Decker to avoid approaching him and call 911 immediately. He faces a maximum of life in prison without the possibility of parole.

Authorities are offering a reward of up to $20,000 for information leading to his arrest.

“We want a peaceful resolution to this, but we’re not going to relinquish our efforts and give up any effort that we could proceed to track you down,” Morrison said at a news briefing Wednesday. “So please turn yourself in. Let’s wrap this up and do what’s right for your kids.”

Anyone with information is asked to call the Chelan sheriff’s tip line at 509-667-6845 or submit information online at https://www.co.chelan.wa.us/sheriff/forms/submit-a-tip.

Fox News’ Christina Shaw contributed to this report.