The decision issued by the council specifically cited provisions in the law that allow records to be classified as protected if releasing them "reasonably could be expected to interfere" with an investigation, deprive a person of a fair trial or disclose sources.
"After viewing them it was very apparent to us that releasing them at this time could be reasonably expected to hamper an ongoing investigation," Rushton said.
Rushton also said the council understands the family's heartbreak and that its "hopes and prayers" are that there will be an ultimate resolution of the case.
Seattle attorney Anne Bremner, who represents Susan Powell's parents, previously said her clients would file a lawsuit if West Valley City refused to provide the records.
"The decision by the WV Cy Council to deny our request for records in the Cox Powell case is disappointing," Bremner said in a statement released via Twitter on Tuesday. "We will press on."
Susan Powell was last seen at her West Valley City home on Dec. 6, 2009. Her husband Josh Powell told police she was in bed when he left their home around 12:30 a.m. on Dec. 7 with their two young sons to camp in the desert. Susan Powell is still missing and has not yet been declared dead.
Josh Powell was the only person of interest in the case until he killed himself and his two sons in a fire on Feb. 5 of this year.
Bremner said Chuck and Judy Cox, Susan's parents, want to review the documents for two reasons: to see if there are clues that might solve their daughter's disappearance and for possible use in a potential civil lawsuit.
The police department and the city manager denied the request earlier this year, but Bremner appealed those decisions to the city council. She argued at a public hearing last Tuesday that there are no privacy or investigative concerns that warrant not releasing the files.
Bremner also told the council the piecemeal release of information in the case has been like a "knife to the heart" to her clients.
But Clint Gilmore, legal adviser to the West Valley City Police Department, said release of the records could jeopardize its ongoing investigation.
"We want to solve this case," Gilmore said. "That is our purpose. The case is still active and we are pursuing it."