Nampa Police say Alfredo Martinez, 39, is now facing charges of second degree murder, destruction of evidence, and failure to notify of a death.
According to court documents, Martinez told police he hit Selena Thomas with a hammer, then when she charged at him he pushed her and she fell and struck the back of her head on a dresser.
He made his first court appearance Friday when a judge set his bail at $5 million.
Martinez was arrested last week on an unrelated probation violation charge and has been in the Canyon County Jail since then.
The maximum penalty for second degree murder is life in prison. He's scheduled to make his next court appearance Sept. 12.