Biendl, 34, was found strangled Jan. 29 in the prison chapel at the Washington State Reformatory in Monroe.
Inmate Byron Scherf, 52, a convicted rapist serving a life sentence without the possibility of parole, is the prime suspect in the attack.
Monroe police must wrap up their criminal investigation before other agencies can delve into the case. Police served more search warrants in the past few days and are wrapping up interviews and collecting evidence, Monroe police spokeswoman Debbie Willis said.
"They're slowing down, but it's continuing," she said Tuesday.
The newest search warrants were for records and paperwork documenting Scherf's life, she said. That includes records for housing, education and his brief stint in the military. They also are looking through his medical records, including his history of medications and psychological evaluations.
As of Tuesday night, Scherf had declined to speak with investigators, she said.
Monroe police will forward their completed investigation to Snohomish County prosecutors. Prosecutors will decide on charges. Killing a corrections officer can lead to the death penalty in Washington.
Monroe Correctional Complex Superintendent Scott Frakes said he must wait until police are finished before investigating what happened the night Biendl died. Among other things, he wants to know why it took more than an hour to find Biendl after Scherf was apprehended in the chapel lobby.
Gov. Chris Gregoire wants an independent review by the National Institute of Corrections, an agency within the U.S. Department of Justice.
The state Department of Labor and Industries also is conducting an investigation. It will determine whether state workplace safety laws were violated, agency spokesman Hector Castro said. They're required by law to wrap up the investigation in six months. If they find something wrong, they can issue citations and fines.
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