He planned it for a year, laid in wait for an hour then the following from the report I've linked:
"They (the police) tried to open the car doors, but finding them locked, they smashed its windows, raised the door plunger and dragged the defendant from the vehicle, arresting him on suspicion of attempted murder. He replied 'Yeah, I'm 100% guilty of that'," said PC Sullivan, adding the boy had "appeared to be smiling". He said the boy told officers: "I've done what I wanted to do, as scummy as it is."
I think his intent is clear on the attempted murder charge.
The defendant, 16, told armed police the situation was "exciting", a court hears.
www.bbc.com