Jabrill Mara had done a lot of living for a 20-year-old.

He dropped out of high school for a year so he could take care of his newborn daughter. Then he went back and finished school, where he also played nose tackle on the football team. He wrote and recorded hip-hop songs. He had served an internship at a car-repair shop and was set to begin full-time work there this week.

But last week, police found him bloodied and staggering along the Nutley Street ramp to Interstate 66 in the Vienna area of Fairfax County. State troopers thought maybe he had been hit by a car and called for an ambulance. When he got to Inova Fairfax Hospital, though, they found he had been shot twice in the back of the head.

Mara lived for two days before dying Dec. 29. His close-knit family, including his longtime girlfriend, doesn't know what to tell his 2-year-old daughter, Amari.

"They were like Mutt and Jeff," his mother, Deborah Mara, said Tuesday. Whenever Mara needed a backup, he would turn to his daughter and yell, "Right, Amari?" and the toddler would respond, "That's right Daddy."

Virginia State Police are investigating the case because Mara was found on an interstate highway, where no vehicle, weapon or witnesses have been found. Police spokeswoman Corinne Geller said investigators had gotten "some really good tips" but no arrests have been made.

Mara was the youngest of Deborah Mara's three children and grew up in her townhouse off Creedmor Drive, near Rolling Road in the Springfield area. It was "the Kool-Aid house," Deborah Mara said, because neighborhood kids rambled in and out at all hours, playing video games, listening to music and watching movies with Jabrill as the master of ceremonies and his mother supervising.

Jabrill Mara was known to the older neighbors for regularly shoveling snow and running errands for those who needed help, his mother said. He also frequently fixed bikes and tinkered with cars.

Mara attended Cameron Elementary School, Key Middle School and Robert E. Lee High School. In his freshman year, he started dating Carina Winston, and she said they never really separated.

"He's the person I called for everything," Winston said. "And he listened. And he remembers everything. We broke up a couple times, but I talked to him every day on the phone. He always saw the big picture. He always thinks before doing anything."

In the couple's junior year, Winston got pregnant. She delivered in September of their senior year, and Mara agreed to stay home with the baby while Winston continued school.

"He did all the daddy stuff," his mother said. "He was in the house all day. He would fix her hair. He did the feedings. He bathed her. He'd dress her. He was an excellent father."