Authorities expected to release affidavit explain why they think Colorado man killed his family

FREDERICK, Colo. -- On Monday, authorities in Colorado are expected to release an affidavit explaining why investigators believe 33-year-old Christopher Watts killed his pregnant wife and two young daughters.

Christopher faces one count of first-degree murder after deliberation, two counts of first-degree murder - position of trust, and three counts of tampering with a deceased human body, after the bodies of his wife, 34-year-old Shanann Watts, and two daughters, 3-year-old Celeste and 4-year-old Bella, were found on the property of Anadarko Petroleum, one of Colorado's largest oil and gas drillers.

Records show Christopher was employed by the company in 2015.

Officials said the bodies of the young girls were found inside oil and gas tanks that "were mostly full." Investigators believe Christopher placed the girls in there to conceal the smell from passersby.

Shanann was reported missing on Aug. 13 by her friend Nickole Atkinson after she missed a doctor's appointment.

Atkinson said she felt something was off and called police.

Atkison spoke exclusively with Good Morning America (GMA), saying things almost seemed too perfect.

Tune in to GMA Monday morning where she will be speaking out on troubling signs and the moment she told Christopher she was calling police.