Two missing Kansas women were killed over a custody dispute involving an anti-government group known as "God's misfits", according to prosecutors.
The women, Veronica Butler, 27, and Jillian Kelley, 39, vanished on 30 March. Their car was later found along with evidence suggesting foul play.
Two bodies were found on Sunday and are being formally identified.
Four people, all belonging to the "misfits" group, have been arrested on kidnapping and murder charges.
According to prosecutors, Ms Butler and Ms Kelley had arranged with the grandmother of Ms Butler's children to meet at a highway intersection in Oklahoma to pick up the two children - aged six and eight - and take them to a birthday party.
Ms Butler's family found their car a short distance from the location of the meeting.
"Blood was found on the roadway and the edge of the roadway," court documents say. "Butler's glasses were also found in the roadway south of the vehicle, near a broken hammer. A pistol magazine was found inside Kelley's purse at the scene, but no pistol was found."
The four people arrested are the children's grandmother, 54-year-old Tifany Adams, her boyfriend Tad Callum, 43, and two others identified as Cole Twombly, 50 and his wife Cora, 44.
Prosecutors say the four people are part of a larger group which they refer to as "God's misfits" and that Ms Adams had been involved in a "problematic custody battle" with Ms Butler.
The group had planned to kill Ms Butler at least once before, according to a teenage witness who spoke to investigators.
That plan allegedly involved throwing an anvil through Ms Butler's windshield while driving "because anvils regularly fall off work vehicles".
Authorities believe that the killings were pre-planned, with Ms Adams buying three disposable "burner phones" to communicate ahead of the incident.
"All three phones were at the area where Butler's car was located and the last known location of Butler and Kelley," the affidavit notes.
Additionally, Ms Adams is alleged to have purchased five stun guns.
A search of her phone later revealed she had searched for "taser pain level, gun shops, prepaid cellular phones and how to get someone out of their house", according to the affidavit.
It is unclear where the two children were during the 14 days of the search. Ms Adams allegedly told investigators that they had been left in the care of another couple, who authorities believe regularly held "God's Misfits meetings."
The two bodies were discovered on Sunday in Texas Country, Oklahoma. Authorities have yet to formally identify them.
All four suspects remain jailed in Texas County without bond.
"This case did not end in the way that we had hoped," Oklahoma State Bureau of Investigation director Aungela Spurlock said on Monday. "It has certainly been a tragedy for everybody involved."
