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The man accused of fatally shooting six family members execution-style and critically wounding a seventh is undergoing a mental evaluation as Texas authorities try to unravel the motivation for Wednesday's grisly rampage.

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Ron Lee Haskell, 33, is charged with capital murder after driving to relatives' home in the Houston suburb of Spring and shooting seven family members, including five children. Police said he may have been set off by a domestic argument involving a divorce.

Dead are two boys, 4 and 13; and two girls, 7 and 9; along with a 39-year-old man and a 33-year-old woman identified as Stephen Stay and Katie Stay, NBC affiliate KPRC reported. A 15-year-old girl was also shot and remains in the hospital.

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Documents read in court Thursday laid out the tragic events: Haskell went to the Spring home looking for his ex-wife. When he first got there, the 15-year-old girl opened the door and she told him her parents weren't home. He left, but later returned, forcing his way inside. He then tied up the girl and waited for her parents and the other children to arrive. When they did, he also tied them up and asked where his ex-wife was.

They told him they didn't know. Then, he allegedly began shooting them one by one in the back of the head. A bullet fractured the 15-year-old's skull but she wasn't killed — and she survived by playing dead. When he left, she called 911 and was able to identify Haskell, her ex-uncle.

A sheriff's spokesman said the gunman's ex-wife was out of town during the incident, The Associated Press reported.

The wounded 15-year-old girl was flown to a hospital in critical condition, but she was able to identify the suspect and tell authorities where he might be going next, Harris County Constable Ron Hickman said. The AP reported that a sheriff's deputy said the girl told authorities her grandparents were the next target.

Police were able to intercept him and stop him in the cul-de-sac after a 20-minute chase. Police surrounded the vehicle as they negotiated with Haskell until he surrendered just after 10 p.m. During the standoff the suspect held a gun to his head, Hickman said.

"It appears this stems from a domestic issue with a breakup in the family from what our witness has told us," Assistant Chief Deputy Constable Mark Herman of the Harris County Precinct 4 Constable's Office told reporters, according to the AP.

Deputy treated for possible heat exhaustion as shooting suspect standoff in NW Harris County continues. pic.twitter.com/nuWORt3uBZ — Phillip Mena (@phillipmenaKPRC) July 10, 2014

Natascha Bass, a family friend of the Stays, told NBC News that they were “good people,” and Stephen Stay was supporting his family by starting his own brokerage firm. Bass said she decided to work for Stay after getting her real estate license.

“If I’m dealing with a client who is behind on their payments, the first words out of his mouth are, ‘I hope they’re OK. I hope they get back on their feet financially,’” Bass said. “He is one of the most kind-hearted people, never thinks anything negative.”

“They were just good people,” she added, “and it’s so surreal that this happened.”

The Associated Press contributed to this report.