The father of two young girls found submerged in oil tanks after being missing for days told authorities his pregnant wife killed the children after learning he wanted a separation, and that he erupted in rage after witnessing the killings and strangled their mother inside the family's suburban Denver home, according to court documents.

Days after letting police inside his home so they could help find his missing family, Christopher Watts told investigators "he would tell the truth."

Watts first asked to speak with his father then admitted to killing his wife, Shanann. Watts told police in court papers released Monday that he killed her after witnessing her strangling one of the girls on a baby monitor. The other child had already been killed by the woman, he said.

Watts, 33, faces three first-degree murder charges, two counts of murdering a child under 12, one count of unlawful termination of a pregnancy and three counts of tampering with a deceased human body. He is scheduled to appear in court on Tuesday and is being held without bail.

District Attorney Michael Rourke declined to answer questions about the case Monday but said his office has three prosecutors working on it. Rourke also said it was too early to discuss whether he will seek the death penalty.

Police first visited the family's house on Aug. 13, after a friend asked officers to check on Shanann Watts. She had missed a doctor's appointment and wasn't answering calls or text messages hours after returning home after a business trip, the friend reported.