A stunned community watched the investigation unfold.
"We have not recovered a weapon. The deceased's personal belongings were still inside the vehicle, so at this point we don't have motive or a suspect," said Lt. Greg Wilkerson, with the Little Elm Police Department.
Neighbors said they heard gunshots around 10:30 p.m. or 11 p.m. Saturday.
Just before 11 a.m. Sunday a friend found Cook's car in the parking lot.
"He made a U-turn, came back into the parking lot, and found out that he was deceased," said Wilkerson.
Ryan was a senior at the Education Center Charter School. He was on track to graduate in May and just purchased his cap and gown on Friday.
"He had a countdown on his desk, so he could count down until he graduated," said Dr. Lisa Ashmore, Superintendent of Student Services.
Cook was also athletic, playing on both the school's flag football and basketball teams. He worked part time at the body shop next door to the school and wanted to be a mechanic someday.
"He was thinking about opening and running his own body shop," said Lee McLaren, principal of the Education Center Charter School.
"Sad kids, sad parents, sad staff. Something like this hits and it always hits hard," said McLaren.
Those who knew him said his positive attitude made him popular at school. They said returning to class without him will be difficult for everyone.