A Minnesota woman who police say was driving under the influence when she hit an Amish buggy and horse, killing two children, tried to get her twin sister to take the fall, police wrote in court documents obtained by USA TODAY on Wednesday.

Samantha Petersen, 35, was charged Monday with 21 counts, including criminal vehicular homicide and leaving the scene of the crash on Sept. 25 in Stewartville, about 100 miles south of Minneapolis. No attorney was listed for her in court records.

Two children, 7-year-old Wilma Miller and 11-year-old Irma Miller, were killed while their 9-year-old brother and 13-year-old sister were seriously injured, according to the Associated Press. Drug tests later showed that Petersen was under the influence of methamphetamine, amphetamine and THC, according to a probable cause statement written by sheriff's Sgt. Daniel Dornink.

The Fillmore County Sheriff's Office told USA TODAY that Petersen had not yet been arrested as of Wednesday evening. The sheriff's office is planning on holding a news conference about the case on Thursday.

What happened on Sept. 25

Police say that Petersen was driving between 63 and 71 mph in a 55-mph zone at the time of the crash, which also killed the horse that was pulling the buggy with the four siblings.

The 9-year-old who survived the crash sustained serious injuries that included a broken left shoulder, lacerated kidney, torn spleen, concussion, and slight bleeding in his brain. The 13-year-old was left with facial scarring.

A GoFundMe for the family raised $90,000 and said that the kids had been on the way to school when the crash happened.

When police arrived, both Petersen and her twin sister, Sarah Beth Petersen, were at the scene. Sarah Beth Petersen told police that she was the one driving, while Samantha Petersen said she had just arrived to the crash scene after her sister called her, Dornink wrote.

Police say it turned out to be the other way around.

Petersen becomes prime suspect

An investigator who had begun interviewing Sarah Beth Petersen was recording their conversation when he briefly left, Dornink wrote, adding that Samantha Petersen then walked over to talk to her sister.

Unbeknownst to them, they were being recorded.

“I think that one of the guys is onto me but I don’t really care … There’s no way they would ever know the difference between the two of us so they can’t tell," Sarah Beth Petersen says, according to Dornink.

Police recovered the recording of a 911 call that came from Samantha Petersen's phone, during which she sounded "emotional and upset," and "can be heard saying, 'I didn't see them coming up over the hill,'" he wrote.

Additionally, police say Samantha Petersen called the human resources department at her work shortly after the car wreck.

“I (expletive) up ... I just killed two Amish people. They were kids ... I just hit a (expletive) buggy ... I’m not sober ... I’m high on meth," she said, the HR manager later told police, Dornink wrote.

Police also say they recovered text messages between Samantha Petersen and a friend. The friend texts Petersen about how a little girl had been killed, to which she replies, according to police: "I don't think you realize that I did that ... I hit that Amish buggy and killed two people... Made Sarah take the fall for it so I wouldn't go to prison."

Police say they also found various internet searches on Petersen's phone, including: “What happens if you get in an accident with an Amish buggy and kill two people?"

Court case moves forward

Among the 21 charges against Samantha Petersen are: criminal vehicular homicide, operating a vehicle with negligence and under the influence, leaving the scene of a crash, failing to provide insurance, careless driving and speeding.

Court records show that she was previously convicted of drunk driving in October 2015 and impaired driving under a controlled substance in August 2018.

If convicted of the new charges, she could face decades in prison. She's due in court on March 25.

Her twin hasn't been charged, AP reported.