A man in a pickup truck pulled up next to a car that was leaving a Houston-area Walmart parking lot and started shooting, killing a 7-year-old girl inside the car and wounding the girl's mother, authorities said Sunday.

Authorities are still searching for the gunman, described as a bearded white man, possibly in his 40s.

Authorities are searching for a red pickup truck, left, in connection with the fatal shooting Jazmine Barnes, right. KHOU

Harris County Sheriff Ed Gonzalez said the girl who died was 7-year-old Jazmine Barnes. He said her mother, 30-year-old LaPorsha Washington, was shot in the arm but survived her injury. Washington's three other daughters were in the car at the time of the shooting, CBS affiliate KHOU reported.

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It wasn't immediately clear what prompted the Sunday morning shooting. The car sped away before it came to a stop and the woman called 911, authorities said. Authorities are asking the public for tips and appealing to nearby residents and businesses to review surveillance video for the red pickup truck.

The Sheldon Independent School District identified the girl as a second-grader at the nearby Monahan Elementary School.

Sheriff's Maj. Jesse Razo said the other girls who were inside the car when the shooting happened were "shaken" and "devastated." One, 6, was injured by shattered glass, and the two others were uninjured, KHOU reported.

"We're going to use all resources available to bring this killer to justice," Razo told reporters at the scene. "And I urge you, whoever did this, you know who you are, please turn yourself in now because we will be looking for you, we will locate you, we will find you."