A man accused of killing his estranged wife and two stepchildren fatally shot himself Friday as he drove into a lake after a nearly seven-hour standoff, police said.

When a wrecker pulled the submerged car out of Lake Arlington, officers saw that Arthur Jackson was dead and had a head wound, said Arlington Police Lt. Blake Miller. No officers had fired any shots, he said.

"Obviously, he was a desperate man," Miller said.

Earlier Friday, Jackson dropped off his bloody but unharmed 4-year-old daughter at an Arlington church, where an alarmed worker called police after hearing him say he had killed some people and might kill more, Miller said.

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Police in nearby Fort Worth then went to his one-story brick house and found the bodies of the woman, her 13-year-old daughter and her 10-year-old son, Fort Worth Police Lt. Dan Draper said. All of them were shot to death, he said. Their names were not released.

The standoff started about 12:30 p.m. after police, who had obtained a list of his relatives from another relative who worked at the church, found the armed man parked in an Arlington driveway. The department's SWAT team joined officers there and quickly surrounded Jackson, using an armored police vehicle to block him in.

As Arlington police talked to Jackson over a loudspeaker and by cell phone throughout the afternoon, he sometimes held the gun to his head, Miller said. He was agitated but also talked about surrendering and "about things being perfect" at times, Miller said.

"He is very worked-up right now," Miller said Friday afternoon. "We are just trying to work through this with him. ... We're trying everything we can to end this peacefully."

During negotiations, Jackson, 32, suddenly drove around the police cars and through a yard, speeding out of the neighborhood, Miller said. He led police on a high-speed chase before shooting himself as he drove into the lake, Miller said.

Hale Elementary School, just across the street from the standoff area, was locked down and the 640 students were moved to the cafeteria for the afternoon, said Arlington schools spokeswoman Veronica Sopher. By early evening, most students had been picked up by their parents after leaving though back doors, she said.

Fort Worth police, who issued capital murder warrants for Jackson on Friday afternoon, were called to the couple's home at least twice since last month, Draper said.

In late September, Jackson called and said he was afraid the girls were home alone because no one would answer the door, Draper said.

A week ago, his wife called Fort Worth police and said her estranged husband was knocking on the door, ringing the doorbell and would not go away. But Jackson was gone when police arrived, Draper said.

The slayings shocked neighbors in this middle-class neighborhood of one-story brick houses and well-kept lawns.

A woman who knew the family arrived at the house Friday afternoon, then began wailing and collapsed in the street after hearing of the killings. As a police officer tried to console her, she screamed: "Why did he do it? He was so happy yesterday."

Neighbors said the children often rode bicycles and walked their dog around the neighborhood. Just last week, the boy was happily playing outside and when he politely asked a neighbor for a glass of water.

"I saw them last week, and they seemed fine," said Schawan Smith, who had gotten to know the family because the 4-year-old attended a Fort Worth day care run by Smith's mother. "I'm heartbroken because my kids played with them."

Jackson was friendly and often played in the yard with his stepchildren, who called him Daddy, neighbors said.

"He was the friendliest guy around," neighbor Tommy Talbott said. "He was a happy-go-lucky guy. Every time I saw him, he had a smile."

Another neighbor, Paula Bledsoe, said Jackson bought her parents' old car and then brought it back to show her elderly mother after he fixed it up. He also frequently asked how her mother was doing.

"It's a total shock, just terrible. I was praying it wasn't the kids," she said.