Why did a mother gun down her daughters in horrific Texas shooting? Mystery of the birthday 'argument' at home where killer mom with a 'history of mental illness' had recently reconciled with her husband

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Clues are emerging that might explain the shocking murder of two Houston girls by their own mother Friday, pointing to a struggling home environment hit hard by mental illness.

Christy Sheats, 42, gunned down daughters Madison, 17, and Taylor, 22, after a family dispute spilled out of their home and onto the street in Fulshear on Friday evening.

Now it has emerged that the mom, who was shot dead by a police officer after fatally wounding her daughters, had a history of mental illness and altercations, and that she and husband Jason, 45, had only recently reunited after a separation.

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Jason Sheats (pictured right) had pleaded with his wife Christy (left) not to shoot their daughters. The pair had just ended a period of separation, and police had previously visited Christy regarding a 'mental crisis'

The 42-year-old shot her daughters Madison (left) and Taylor Sheats (right) after a family dispute Friday

Fort Bend County Sheriff's Office spokeswoman Caitilin Espinosa told People that officers had been to the Sheats' home 'for previous altercations'

Those altercations, she said, involving a 'mental crisis' that Christy Sheats had been undergoing.

However, she would not elaborate on the remarks. 

The Houston Chronicle confirmed that police had visited the house on multiple occasions.

And a neighbor told ABC13 that Christy and Jason Sheats had only recently reunited after a period of separation.

But that reunion led to disaster when a family argument on Friday - which was also Jason's birthday - spiraled into a double-murder that ended with a police officer shooting Christy.

Jason, who was the only family member to survive the incident, though he was taken to hospital due to his distress.

A police officer heard him pleading with his wife before she was shot dead, neighbour Fazz Zainuddin told Click2Houston.

‘[The officer] heard the dad say, "Don’t do this. They’re our kids",' Zainuddin said.

Officers had responded to a 911 call around 5pm on Friday. They arrived to find the two daughters lying outside the home in the 6000 block of Remson Hollow Lane in the Houston suburb of Fulshear.

The mother, who is originally from Decatur, Alabama, was killed by a responding police officer after she refused to drop her pistol, authorities said.

Sheriff Troy Nehls says the shooting was apparently after a family argument, but the reason for the dispute remains unclear.

Nehls says the two younger women had already been shot when a Fulshear police officer arrived and saw the mother with a gun in her hand, apparently preparing to shoot one of her daughters again.

The officer shot and killed her. 

Jason Sheats (center) escaped unscathed but was taken to hospital because he was distraught 

Christy Sheats (pictured) was killed by a responding police officer after she refused to drop her pistol

‘The cops were behind the trees and behind the cars, and they told the mom to put the gun down and obviously she did not,’ Zainuddin said.

He said Christy had walked towards her daughter Madison’s body still holding the pistol.

‘I guess the cop was afraid he was going to shoot her again,‘ he added. 

Authorities have been called to the home multiple times in the past, but it remains unclear why.

One witness said he saw Jason and his daughters running out of their home, ABC13 reports.

The girls were already wounded, the witness told the station, and Taylor then collapsed in the street.

The witness added that he saw the mother come outside with her gun, before going back inside to reload her weapon.

When she returned, she shot Madison in the back, he said.

Madison (right) worked as a babysitter, while Taylor (left) was a student at Lone Star College

Madison was pronounced dead at the scene, while Taylor was airlifted to a hospital in a critical condition, where she later died. 

Christy and Jason Sheats had recently reunited after being separated, another neighbor told ABC13. She said the shooting on Friday was on Jason’s birthday.

Meanwhile, other neighbors in Fulshear expressed shock when they heard of the shooting.

‘The mother was nice,’ one said. ‘You wouldn’t expect if they told you this is what was going to happen.’

Austin Enke, who went to high school with one of the girls, said he thought he heard fireworks at first.

'It's crazy. The neighborhood has never seen this kind of thing before. It's always quiet,’ he told KHOU.

‘This is surprising. They never showed any kind of thing that was wrong with them whatsoever,'

Christy, a business manager at a laser tattoo removal clinic, posted a photo of her two daughters on Facebook in September last year.

Christy (right with Madison left) refused to drop her pistol when authorities arrived on the scene, and a Fulshear police officer was forced to shoot her

She wrote: 'Happy Daughter's Day to my two amazing, sweet, kind, beautiful, intelligent girls. I love and treasure you both more than you could ever possibly know.'

It emerged that she was also an outspoken gun rights advocate.

'It would be horribly tragic if my ability to protect myself or my family were to be taken away, but that's exactly what Democrats are determined to do by banning semi-automatic handguns,' she wrote on Facebook in March.

Tributes poured in for Taylor, who went to Lone Star College, and Madison, a student at Seven Lakes High School, on Facebook on Saturday.

Taylor’s friend Joanna Higgins wrote on their high school alumni page: 'I'm in utter shock. She was so talented and had a heart of gold. God rest her soul and those mourning her loss.'

Madison's former teacher Whitney Mae Bruce wrote: 'My heart is broken this morning to find that my sweet Madison Sheats lost her life.

‘Always positive and smiling, Madison quickly became one of my favorite students four years ago while teaching for the first time in Katy.

'A wonderful student/person/babysitter will be missed enormously. Please pray for her father.' 

Police arrived to find the two daughters lying outside the home in the 6000 block of Remson Hollow Lane