Police say Haskell gathered several children in the home and waited for their parents to come home. He then shot seven people. Six died and one girl survived.
"He came to this location yesterday afternoon ... and came under the guise of a FedEx driver wearing a FedEx shirt," said Harris County Precinct 4 Constable Ron Hickman. "(He) gathered up the children that were here and awaited the arrival of the parents. Sometime later the victims were shot in this residence, and we now learned that Mr. Haskell was married to a relative of the residents of this home."
Authorities described the dead as two boys, ages 4 and 14; two girls, ages 7 and 9; a 39-year-old man; and a 33-year-old woman.
In court Thursday, prosecutors said Haskell tied up the family, placed them face down, and then shot each of them in the head execution style.
Hickman corrected an earlier report that said Haskell was the father of the children. He did not release details of Haskell's relationship to the family, but described the adults killed as the children's parents.
Deputies said a 15-year-old girl suffered a bullet fracture to her skull. They said she played dead until Haskell left and then alerted authorities that he was on his way to her grandparents' home to kill more relatives.
A standoff ensued when deputies cornered Haskell in a cul-de-sac in a nearby neighborhood. He surrendered after four hours.
During the standoff, Deputy Thomas Gilliland said there were "two hours of constant talking with a man armed with a pistol to his head and who had just killed six people."
Gilliland described the man as in his 30s with a beard "and cool as a cucumber." He said that when he and other officers first approached, the man was "just sitting in his car looking out at us."
The surviving teen girl was in "very critical condition" at Memorial Hermann Hospital in Houston as of late Wednesday, Gilliland said.