A female correctional officer at a Washington state prison was fatally strangled and an inmate who told officers he had planned to escape is under investigation, authorities said Sunday.

Jayme Biendl, 34, was discovered late Saturday night after workers at the Monroe Correctional Complex noticed her keys and radio were missing, according to a statement from the Washington State Department of Corrections. Staff at the prison immediately went to where she worked and found her unresponsive, it said.

Emergency responders declared Biendl dead at the scene shortly before 11 p.m. PT, the department said.

She had been strangled, according to Chad Lewis, a department spokesman.

Also Saturday night, a prison inmate was reported missing during a routine count, the department said. He was later found in the chapel lobby and told officers he had planned to escape, but changed his mind.

The inmate, who Lewis identified as Byron Scherf, has since been taken to a segregation unit. The entire complex was on lockdown Sunday as officers investigate the incident, the statement said.

Police are interviewing Scherf as a suspect in the officer's death, Lewis said.