A 13-year-old girl with Down syndrome was killed by a hit-and-run driver shortly after midnight Sunday as she crossed Hempstead Turnpike, police said.

Family members said she wandered away from her Levittown home in what may have been an attempt to visit her grandfather a couple of miles away in Hicksville.

Bryanna Soplin was crossing the six-lane roadway at Gardiners Avenue at 12:02 a.m. Sunday when she was struck by a minivan, Nassau County police said. Investigators described the vehicle as a blue 2011 to 2013 Chrysler Town and Country that left the scene by continuing east on Hempstead Turnpike and then north onto the Seaford-Oyster Bay Expressway.

"He should've stayed there and helped her," Bryanna's mother, Jennifer Curuchaga, said of the driver.

"He just let her die," Curuchaga, 33, told News 12 Long Island as she sobbed. "Please, I know it won't bring my baby back, but he needs to pay for what he did."

Bryanna may have been trying to visit her grandfather, said the girl's father, Julio Soplin, 35, of Glen Cove.

"Right now, I'm very distraught," Soplin said.

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His daughter, who he said had Down syndrome, "loved everything."

"She liked to do karate right now," he said. "She was doing that two times a week. She was happy."

Bryanna left the house only once before during the night, when she was 5 or 6 years old, Julio Soplin said. At that time, she left to go play in a park, he said.

The Hempstead Turnpike intersection where Bryanna was hit is 1.9 miles south of the home of her grandfather, Carlos Curuchaga. Bryanna was struck as she crossed from the south side of Hempstead Turnpike to the north, police said.

Bryanna was taken to Nassau University Medical Center in East Meadow with head and body trauma and was pronounced dead by hospital staff at 4:30 a.m., police said.

About a dozen family members, friends and neighbors quietly gathered at the grandfather's house throughout the afternoon Sunday. They walked along the porch and in the front yard of the small beige home.

Carlos Curuchaga declined to comment and asked that the family's privacy be respected.

Jennifer Curuchaga told News 12 she woke up shortly after midnight with "a gut feeling." She ran upstairs and found her daughter wasn't in bed. The back door was unlocked, she said, and she called police to report her daughter missing.

"Five minutes later, they found her dead in the street," Jennifer Curuchaga said. "She was such a happy, beautiful girl who made everyone, everyone's life special."

James Grossane, superintendent of the Levittown school district, where Bryanna was a student in the Wisdom Lane Middle School, said grief counselors will be available Monday for students and staff.

"We are extremely saddened to learn of the tragic death of one of our Wisdom Lane students," Grossane said in a statement. "The Levittown Board of Education, administration, faculty and staff extend their deepest condolences to Bryanna's family and friends during this difficult time."

Hempstead Turnpike has long been one of the deadliest roadways for pedestrians on Long Island. Hundreds of deaths and injuries have occurred along the busy stretch, according to transportation experts and Newsday reports.

The New York State Department of Transportation has not put in enough traffic-safety measures along the road, Ryan Lynch, associate director of the Tri-State Transportation Campaign nonprofit advocacy group, said Sunday.

"They've tinkered around the edges," Lynch said. "I'm frustrated . . . We haven't done all we can to make these more preventable."

He said while the state has put in medians and crosswalks in some sections of the 16-mile road, he would like to see consideration given to narrowing the road from three lanes in each direction to two, as well as other measures to slow traffic. More medians could also be put in, and pedestrian islands could be installed that can serve as safety refuges during crossings.

Hempstead Turnpike is designed to move cars as quickly as possible, he said. "At the same time, there are destinations that pedestrians go to, cyclists go to, and we still see all these fatalities happen. New York State DOT has to make these more preventable."

Representatives of the transportation department did not immediately respond to a request for comment.

Police ask anyone with information about this case to contact Nassau County Crime Stoppers at 800-244-TIPS. All calls will be kept confidential.

With Deon J. Hampton and Jennifer Barrios