A mother shot and killed her two young daughters after plotting for weeks, police say

'Why did I do that, Jake?'

The first EMS call came in at 11:29 p.m. Wednesday.

"I want to get somebody out here to check my wife out," Jacob Henderson said, his voice calm and even. He didn't think his wife was trying to commit suicide, he told the dispatcher, but she was "freaking out like somebody is out to get her."

Seven minutes later, Henderson called again. His wife was "fine now," and he wanted to cancel his earlier request for help.

Still, deputies from the Henderson County Sheriff's Office came to Henderson's home in Mabank, Texas, roughly 55 miles southeast of Dallas. It was the home he shared with his wife, Sarah Nicole Henderson, 29, and her daughters, ages 7 and 5.

"A male and female told the Deputies they were fine and no one was in danger or jeopardy," read a news release from the Sheriff's Office.

Henderson's next call came in at 2:24 a.m. Thursday. Choking back tears, panting for breath, and at times wailing, Henderson told the 911 dispatcher that his wife had shot her children.

And now, Sarah Henderson was clutching onto her neck, as if trying to choke herself. She kept trying to pry back the gun Jacob Henderson took away from her.

In the background of that distraught 911 call, Sarah Henderson can be heard asking: "Why did I do that, Jake?"

He had fallen asleep and awoken to hear his wife say, "Jake, I shot the kids," Jacob Henderson told the dispatcher. In his 911 call, Jacob Henderson alerted police to what they would find: the girls, reported to be 7-year-old Kaylee and 5-year-old Kenlie, had been shot in the head.

Recordings of Jacob Henderson's EMS and 911 calls were released by the Sheriff's Office on Friday.

County Sheriff Botie Hillhouse told The Washington Post that officials had yet to determine a motive in the killings. Hillhouse said officers had been dispatched to the house in 2015 for a "verbal disturbance," but that all they found was Sarah Henderson standing in her yard, arguing with someone over the phone.

"We hadn't had much to do with her until Wednesday night and then again Thursday," Hillhouse said.

CBS News reported that Texas Child Protective Services confirmed it had been in contact with the family six years ago, but that other details were confidential.

Sarah Henderson has been charged with one count of capital murder, with another capital murder charge pending, officials said. She was arraigned Friday morning with bail set at $2 million and remains in jail under suicide watch. Hillhouse said the punishment for capital murder in Texas is life in prison or the death penalty.

The gruesome case took another dark turn Friday when investigators announced Sarah Henderson had planned for at least two weeks to kill her children, though authorities did not provide further details to support this claim. She had also intended to kill her husband, "but the entire crime did not go as planned," a news release said. ABC News quoted Hillhouse as saying that the gun malfunctioned when Sarah Henderson tried to kill Jacob.

"She was very matter of fact, to the point and just didn't show any remorse," Hillhouse said of officials' interviews with Sarah Henderson.

Hillhouse said Jacob Henderson was not the biological father of the victims and has been cooperating with authorities. He added that Sarah Henderson has another son who lives with his father outside the county.

The Texas Rangers, Child Protective Services and the Henderson County District Attorney's Office are assisting with the investigation. It was not clear if Sarah Henderson had obtained an attorney.

A neighbor, Jaylyne Palmer, told NBCDFW that she had never had a conversation with Sarah Henderson, but that the girls would ride their bikes through her driveway.

"They would draw pictures and put them in the mailbox for us," Palmer said.

Jacob Henderson's 911 call recorded Sarah Henderson saying, "I'm sorry."

"Why though?" Jacob Henderson cried. "Why? Why? Why?"

Then he saw flashes of red and blue light come down the street.

"They're here," he told the dispatcher, before hanging up.