At this point, detectives have not said why they believe Cohn planned to kill his wife. There is no known history of domestic violence and police had not been called to the Cohns' home before Wednesday.
"As far as our investigation goes, we know who did it and what happened," Clark said hours after officers discovered Linda's body and arrested Cohn. "We just don't know why."
Neighbors were stunned to learned that Cohn allegedly killed his wife.
Police have not released Cohn's 911 call. That could happen as soon as Thursday afternoon if the Maricopa County Attorney's Office gives its approval.
Cohn is undergoing psychiatric evaluation.
First-degree murder is a class 1 felony. A conviction can carry the death penalty or life in prison.