Around 4 a.m. on December 3, 2012, authorities say 24-year-old Mary Agnes Leider sat in the front passenger seat of her Dodge pickup while her brother Wally drove down Highway 313 south of Hardin, Montana.
According to court documents, they had been out drinking that night and were on their way home. Mary's 3-year-old daughter Tennielle Big Day sat quietly on her lap.
Wally Leider later allegedly told authorities that as he drove Mary reached for the passenger door, opened it and threw Tennielle out of the moving vehicle. The child died from her injuries.
A federal criminal complaint for second-degree murder was filed against Mary Leider on Tuesday in connection with her daughter's death.
A probable cause affidavit stated that the Big Horn County Sheriff's Office received 911 calls at approximately 4:06 a.m. on December 3 from distraught individuals in the area of mile marker 11 on Highway 313. Responding officers found Mary Leider and her brother Arland sitting on the side of the road, "crying uncontrollably" the affidavit said.
At the time, Leider allegedly told the first deputy on the scene that her baby had been hit by a vehicle and was "gone," according to the affidavit. Soon after that, however, the deputy was dispatched to respond to another 911 call at mile marker 19 on the same road.
There, he was met by Wally Leider and their mother, Georgina Denny, who showed him Tennielle Big Day's lifeless body, court documents stated.
According to court documents, Mary Leider told authorities that she had been arguing with Wally while he was driving home and she kept telling him to slow down. She said he stopped the vehicle and she hit her face on the dashboard. She allegedly claimed she could not remember how Tennielle was injured after that.
Wally Leider allegedly told investigators that Mary threw Tennielle from the vehicle, the probable cause affidavit stated. He said he stopped the truck, got out and saw the girl lying in the road. He believed she was already dead, but he put her in the back seat and drove toward their home, leaving Mary and Arland behind, court documents stated.
According to the affidavit, Georgina Denny told officers she had gone out looking for her children and granddaughter, but she then saw Wally driving down Highway 313 in Mary's pickup truck. They both stopped and Wally showed her Tennielle, who was unresponsive and not breathing, in the truck. Denny said she saw blood coming from the back of the girl's head.
Mary Leider was taken to a hospital for treatment of facial abrasions and to have her blood drawn. An FBI lab determined that her blood alcohol level was higher than .24, the affidavit stated. While at the hospital, she allegedly alternated between claiming that her daughter died in a car accident and saying, "I killed my baby."
Investigators determined that the vehicle had not been in an accident.
Leider made her first court appearance on the second-degree murder complaint Wednesday and waived a preliminary hearing. A detention hearing has not been scheduled.
Court records indicate that Leider is a member of the Crow Tribe and that the crime occurred within the boundaries of the Crow Indian Reservation.
A spokesperson for the Montana U.S. Attorney's Office declined to discuss a possible motive or any other details of the case, citing the ongoing nature of the investigation. Prosecutors plan to go before a grand jury within 30 days and seek an indictment against Leider.
A federal public defender appointed to represent Leider did not return calls seeking comment on the case.
According to an obituary published in the Billings Gazette, Tennielle Big Day was "an active child who loved to play outdoors with her friends. She often enjoyed building castles with her Lego blocks. She loved to dance and was a traditional Crow dancer."