Lewis County, MO - The LaGrange man who brutally killed his wife and infant son admitted to the murders in court.

Twenty-four year old Christopher M. Piersee reached a plea deal with the prosecution. He'll spend the rest of his life in prison but escapes the death penalty.

That means he'll serve life in prison without the possibility of parole in the deaths of his wife and infant son.

The family of Patricia Piersee yelled out "thank you" when Christopher admitted to the murders.

Those members did not want to comment, but four of them showed us matching tattoos that they had gotten for Patricia and baby Landon.

We spoke with the mother of Christopher Piersee...she told us her son suffered from psychosis that was a side effect of a common cold medication at the time of the murders.

We've learned Piercee was on dextromethorphan at the time of the murders. Dextromethorphan is also called DXM or DM, and it's a common ingredient in cold medications.

The murder rocked the small town of LaGrange. Police found the bodies of 21-year-old Patricia "Tish" Yarbrough Piersee, and her five-month-old son, Landon on Feb. 3 after being called to the family's home by Tish Piersee's father.

According to court testimony, investigators found Piersee naked in a bedroom of the family's home with the bodies of his wife and son nearby.

Red crosses were drawn in blood on both victims' bodies.  Lewis County Sheriff's Department Chief Deputy Rob Power testified Piersee believed he was the archangel Michael and referred to his wife as Lucifer and his son as the Antichrist. Power said the words "Lucifer" and "Michael" had been scrawled on the walls in blood.