New court documents filed by defense attorneys for the Colorado man accused of killing his pregnant wife and daughters suggest the young girls were strangled before they were left in an oil well on the property of one of the largest oil and gas drillers in the state.

Chris Watts, 33, was arrested this week on suspicion of three counts of first-degree murder and three counts of tampering with a deceased body in connection with the deaths of his pregnant wife, Shanann, and their children, 4-year-old Bella and 3-year-old Celeste.

The Weld County coroner’s office confirmed bodies found on the grounds of Anadarko Petroleum Corp. — where Watts used to work — are those of Shanann and the missing girls. Court documents obtained by 9 News revealed the children’s remains were discovered in an “oil well filled with crude oil for several days.”

RELATED: Shanann Watts and her two daughters disappear in Colorado

63 PHOTOS Shanann Watts and her two daughters killed in Colorado See Gallery Shanann Watts and her two daughters killed in Colorado A photograph sits amid the tributes as they grow outside the home where a pregnant woman, Shanann Watts, and her two daughters, Bella and Celeste, lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband, Christopher Watts, has been arrested on suspicion of killing his family. (AP Photo/David Zalubowski) Christopher Watts, 33, arrested on suspicion of murdering his pregnant wife and two young daughters, in Frederick, Colorado, U.S., is shown in this handout photo provided August 16, 2018. Weld County Sheriff's Office/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY GREELEY, CO - AUGUST 21: Frank Rzucek the father of Shanann Watts was in court for Christopher Watts arraignment hearing at the Weld County Courthouse on August 21, 2018 in Greeley, Colorado. Christopher Watts faces nine charges, including several counts of first-degree murder of his wife Shanann and his two young daughters, 4-year-old Bella, and 3-year-old Celeste. (Photo by RJ Sangosti/The Denver Post via Getty Images) This photo combo of images provided by The Colorado Bureau of Investigation shows, from left, Bella Watts, Celeste Watts and Shanann Watts. The Frederick Police Department said Chris Watts was taken into custody. Watt's pregnant wife, 34-year-old Shanann Watts, and their two daughters, 4-year-old Bella and 3-year-old Celeste were reported missing Monday, Aug. 13, 2018. The police said on Twitter early Thursday that Chris Watts will be held at the Weld County Jail. He has not yet been charged. (The Colorado Bureau of Investigation via AP) Photo: Facebook GREELEY, CO - AUGUST 21: Frank Rzucek the father of Shanann Watts was in court for Christopher Watts arraignment hearing at the Weld County Courthouse on August 21, 2018 in Greeley, Colorado. Christopher Watts faces nine charges, including several counts of first-degree murder of his wife Shanann and his two young daughters, 4-year-old Bella, and 3-year-old Celeste. (Photo by RJ Sangosti/The Denver Post via Getty Images) Photo: Facebook Christopher Watts is escorted into the courtroom before his bond hearing at the Weld County Courthouse on Thursday, Aug. 16, 2018, in Greeley, Colo. Watts, of Colorado, whose wife and daughters disappeared this week was arrested on suspicion of killing them. (Joshua Polson/The Greeley Tribune via AP, Pool) FREDERICK, CO - AUGUST 16: Terry Warren, of Frederick, taks a moment at a makeshift memorial to Shanann, Bella and Celeste Watts, who have been missing since Monday, is seen outside the family home on August 16, 2018 in Frederick, Colorado. Frederick police have arrested Shananns husband Christopher Watts on suspicion of murdering the three. (Photo by RJ Sangosti/The Denver Post via Getty Images) GREELEY, CO - AUGUST 21: Frank Rzucek the father of Shanann Watts, left, and her brother Frankie Rzucek were in court for Christopher Watts arraignment hearing at the Weld County Courthouse on August 21, 2018 in Greeley, Colorado. Christopher Watts faces nine charges, including several counts of first-degree murder of his wife Shanann and his two young daughters, 4-year-old Bella, and 3-year-old Celeste. (Photo by RJ Sangosti/The Denver Post via Getty Images) Photo: Facebook Judge Marcelo A. Kopcow speaks to the attorneys during the bond hearing for Christopher Watts at the Weld County Courthouse Thursday, Aug. 16, 2018, in Greeley, Colo. Watts, of Colorado, whose wife and daughters disappeared this week was arrested on suspicion of killing them. (Joshua Polson/The Greeley Tribune via AP, Pool) Photo: Facebook Weld County District Attorney Michael Rourke waits for the bond hearing for Christopher Watts to begin at Weld County Courthouse Thursday, Aug. 16, 2018, in Greeley, Colo. A judge has ordered Watts of Colorado who is accused of killing his pregnant wife and two young daughters held in jail without bail. (Joshua Polson/The Greeley Tribune via AP, Pool) Baltasar Gutierrez, left, joins his daughter, Irene Montoya, in talking to reporters after they left a tributes outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) From left, 4-year-old Liberty Bell joins her mother, Ashley, and father Steven as they put a tribute with others outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) FREDERICK, CO - AUGUST 16: Frederick Police Department Chief Todd Norris talks to media on August 16, 2018 in Frederick, Colorado. Frederick police have arrested Shananns husband Christopher Watts on suspicion of murdering the three. (Photo by RJ Sangosti/The Denver Post via Getty Images) Photo: Facebook FREDERICK, CO - AUGUST 16: Colorado Bureau of Investigation Director John Camper talks to media on August 16, 2018 in Frederick , Colorado. Frederick police have arrested Shananns husband Christopher Watts on suspicion of murdering the three. (Photo by RJ Sangosti/The Denver Post via Getty Images) Photo: Facebook Ashley Bell places flowers with the growing number of tributes outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Photo: Facebook FREDERICK, CO - AUGUST 16: Colleen Hendrickson and her grandson Ezra Reed, 3, who lives down the street, place flowers at a makeshift memorial to Shanann, Bella and Celeste Watts, who have been missing since Monday, outside the family home on August 16, 2018 in Frederick, Colorado. Frederick police have arrested Shananns husband Christopher Watts on suspicion of murdering the three. (Photo by RJ Sangosti/The Denver Post via Getty Images) Photo: Facebook Christopher Watts glances back at a Weld County Sheriff's Deputy as he is escorted out of the courtroom at the Weld County Courthouse Thursday, Aug. 16, 2018, in Greeley, Colo. Watts, of Colorado, whose wife and daughters disappeared this week was arrested on suspicion of killing them. (Joshua Polson/The Greeley Tribune via AP, Pool) Photo: Facebook A pump jack sits near the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Photo: Facebook Tributes grow outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Photo: Facebook Tributes grow outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Photo: Facebook Photo: Facebook Photo: Facebook Ashley Bell reacts after leaving flowers among the tributes growing outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Photo: Facebook A photograph sits amid the tributes as they grow outside the home where a pregnant woman, Shanann Watts, and her two daughters, Bella and Celeste, lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband, Christopher Watts, has been arrested on suspicion of killing his family. (AP Photo/David Zalubowski) Photo: Facebook Photo: Facebook Tributes grow outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Photo: Facebook Photo: Facebook Photo: Facebook Tributes grow outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Photo: Facebook Photo: Facebook Irene Montoya of Aurora, Colo., places a bouquet of flowers as tributes grow outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Bella goes Zip Lining today on Field Trip! 😱 Celeste’s pigtails 😂😂😂 Picked up this cutie from school for mommy/daughter lunch. She was excited to tell her daddy all about it. My sweet princess! I love her so much. She went with me this morning to Rise and Thrive and we had a blast! These two little girls are my world! I love them so much, even when they drive me crazy! Tomorrow is the last day Celeste is in 2yr old PreSchool and Bella is in PreK 1. Growing up so fast. Happy Husband Appreciation Day! I couldn’t imagine a better man for us. You spoil us with love an attention! You put up with 3 impatient, demanding women in the house. 🤣🤣 You Work so hard everyday to provide for us. I love you so much and so grateful you hung around when I tried pushing you away in the beginning! 🤣🤣 #HappyHusbandappreciationday Ashley Bell, left, is consoled by her husband, Steven, and 4-year-old daughter Liberty as the woman places a tribute outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Wind 💨 Be Crazy 😜 today! #colorado #windblownhair #windy #beautiful #crazy My world and heart all wrapped up in this photo! . . . . #myworld #myheart #myloves #love #chris #age33 #celeste #age2 #bella #age4 #family #mygirls #instagram #instaphoto #instapic #spring #colorado I love this man more than words can say! He’s my Rock, my love, my biggest fan, supporter and my husband! I couldn’t of hand picked a better man to call my husband and father to our girls! He dreams Big with me, he runs hard with me and he is just flat out friggin awesome! I love you Chris so much! Happy Valentines Day! #8yearsandcounting #love #valentinesday #myman #mylove #forever #sappy Kids are napping, now it’s time for me to brace myself for a Costco Run! 😜😎🤪 thank goodness we Thrive! 🙌🏽Mood Support is being tested this week! Who’s kiddos still nap? 😴 #naptime #thrive #sickkids #christmas #busy #love Love my snuggles! #rarewithcece #wild #fearless #fulloflove #fulloflife #loveher #daughter #blessed FREDERICK, CO - AUGUST 16: Neighbors, who did not want to give names, bring a stuffed dog to a makeshift memorial to Shanann, Bella and Celeste Watts, who have been missing since Monday, is seen outside the family home on August 16, 2018 in Frederick , Colorado. Frederick police have arrested Shananns husband Christopher Watts on suspicion of murdering the three. (Photo by RJ Sangosti/The Denver Post via Getty Images) Photo: Facebook An unidentified young boy places a bouquet of flowers on a pile of tributes outside the home where a pregnant woman and her two daughters lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband has been arrested in the disappearance of the woman and children. Authorities say that they have found the woman's body and believe to know the whereabouts of the two girls. (AP Photo/David Zalubowski) Christopher Watts looks down during his bond hearing at the Weld County Courthouse Thursday, Aug. 16, 2018, in Greeley, Colo. Watts, of Colorado, whose wife and daughters disappeared this week was arrested on suspicion of killing them. (Joshua Polson/The Greeley Tribune via AP, Pool) A photograph sits amid the tributes as they grow outside the home where a pregnant woman, Shanann Watts, and her two daughters, Bella and Celeste, lived Thursday, Aug. 16, 2018, in Frederick, Colo. The woman's husband, Christopher Watts, has been arrested on suspicion of killing his family. (AP Photo/David Zalubowski) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

The official cause of death for each family member remains pending, though motions filed by defense attorney James Merson request the pathologist take DNA samples from the girls’ necks during their autopsies. He noted that he sought out the opinion of DNA expert, Richard Eikelenboom, who maintained that evidence can be preserved despite the bodies being left in oil.

“In my opinion, the presence of oil will not destroy the DNA,” he said, separately referencing techniques used to preserve DNA “after strangulation,” according to the Coloradoan.

Police have not released information on a motive or any additional information in the case. Ahead of his arrest Wednesday, Watts told reporters how much he missed his family — recalling simpler times like when they would go out for dinner and how he’d watch them as they watched cartoons.

In an interview with KMGH, he said his wife returned from a business trip to their home in Frederick around 2 a.m. Monday. When he was asked by a reporter whether or not they argued he said they “had an emotion conversation.”

“I just want them back,” he added. “I just want them to come back.”

Formal charges are expected to be filed on Monday by Weld County District Attorney Michael Rourke. Watts is being held at the Weld County Jail, just north of Denver.