The accident happened last week in Lewisville, and so far, police are coming up with very few leads in the investigation.
Family members describe the victim, 32-year-old Michael Singleton, as smart and fun-loving with a big heart unlike any other.
They say it's hard to understand how someone had the gall to hit Singleton and leave him for dead.
Between 9:45 p.m. and 10:15 p.m. on June 8, Lewisville police say Singleton was crossing Garden Ridge westbound when he was struck by a car going southbound.
That driver took off.
After not hearing from Singleton, his fiancée, Rebecca Edmondson got worried.
A normal 20-minute trip to get something was taking unusually longer than usual.
"I just kept calling and calling and calling," said Edmondson. "He wasn't answering. After an hour and 15 minutes or so, somebody picked up his phone and it was the E.R."
A couple passing by saw Singleton on the ground and called 911.
Singleton was eventually airlifted to Medical Center of Plano in critical condition with a broken pelvis, severed artery and head trauma.
Family members say he died Tuesday.
Investigators say they checked every camera around the area, but the video was either grainy or not helpful, so police have no leads on the driver.
"Where's your heart?" said Edmondson. "Are you human? You took a person's life."
With no answers, all his family members have is grief.
"A parent shouldn't outlive their son, so please come forward if you have information," said Singleton's mother, Sherry Parks.
Police say it's possible the driver didn't realize they hit somebody, but family members say doctors told them that Singleton's injuries suggest he was hit with such force that he flew over the hood, making it impossible for the driver to not know what they did.
Family members hope that someone notices a car with that type of damage and calls police.
Anyone with information is asked to contact the Lewisville Police Department at 972-219-TIPS (8477) or Denton County Crime Stoppers at 800-388-TIPS (8477).
Tips can also be anonymously sent using the keyword "TIPLPD" with your information to 847411.