Christopher Cevilla, father of 7-year-old Jazmine Barnes, speaks during a news conference, Monday, Dec. 31, 2018, in Houston.
Harris County Sheriff Ed Gonzalez tweeted that the suspect was driving a red pickup.
A distraught Washington said, "He intentionally killed my child for no reason".
In addition to the girl and her mother, two teenagers and a younger girl were also in the vehicle, Gonzalez said.
Heartbreaking news surfaced as reports of a 7-year-old girl being shot to death in a Walmart parking lot surfaced.
Deputies said five people were in the vehicle that was leaving a Walmart store when a man pulled up next to it and started firing.
The girl, whom police have not yet publicly named, was killed around 7am on Sunday in a auto alongside her mother and three sisters as the vehicle exited the Walmart on Wallisville Road in northeast Houston.
A mother, daughter and three others were leaving when a male began firing into their auto, according to the sheriff's office.
"The family should be celebrating and spending time together anticipating the new year and instead they're making plans to bury this innocent, precious child", Gonzalez said.
The suspect is described as a white man in his 40s and has a beard. Jesse Razo said the survivors are "shaken and devastated". "He didn't even know who she was", she said.
Authorities were working to determine whether the shooting was random or targeted. Another child in the auto suffered minor injuries from glass fragments.
The gunman's motive remains unknown.
The Sheldon Independent School District said Jazmine was a second-grader at Monahan Elementary and "will truly be missed by all students and staff".
"We are going to do everything in our power to make sure that we locate the individual responsible for this heinous crime", the sheriff said.