FREDERICK, Colo. -- Prosecutors in Colorado are preparing to file formal charges of first-degree murder and evidence tampering against Christopher Watts, who is accused of murdering his pregnant wife and two daughters.

In the latest court motions filed Friday, Watts' attorney is asking for DNA samples to be taken from the two girls. What the defense wants to do with the samples is not known.

The paperwork also notes that the children were found in an oil tank filled with crude oil and had been there for several days.

Chris Watts mugshot CBS Denver

The 33-year-old is being held in a Colorado jail after he reportedly confessed to killing his pregnant wife Shanann and their two daughters -- 3-year-old Celeste and 4-year-old Bella.

Their bodies were discovered on Thursday on the property of one of his worksites.

Earlier this week, Watts' told reporters he had no idea where his family could be, and he pleaded for their safe return.

"It's not something I could ever fathom would ever happen in my lifetime," he said.

Shanann Watts was last seen at 2 a.m. Monday by a colleague who dropped her off from a work trip. Her brother took to Facebook to lash out at Watts, saying "I just want 30 seconds alone with that heartless psychopath. May Satan have mercy on his soul."

Kelley Trippy, a neighbor, said the murders have shocked the community.

"You don' know someone, at all, until you find out that they have done something so evil," she said.

She is still trying to make sense of what seemed like perfect marriage and home life.

The couple had faced financial problems, filing for bankruptcy in 2015, but seemed to be making progress and were planning a trip in October.