Police are appealing for anyone who saw or knows anything about Sunday's crash where two teenage girls died to come forward.
They have not ruled out more charges. They are not saying whether they think that more people were in the smashed-up car than the two dead teenagers, the boy who has appeared in court plus a male passenger.
Police said officers were called to the Monaro Highway, just south of the Lanyon Drive intersection, about 8am on Sunday, when they found the girls - aged 14 and 15 - dead in the car.
It is unclear, however, exactly when the crash happened.
The two teenage passengers were thought to have died some time before police and ambulance crews arrived at the scene.
Acting Inspector Travis Mills said teenagers should not get into a car if they thought it was unsafe.
"I would urge passengers to ask before jumping into a vehicle," he said.
"These young girls were going to return to school today."
"Our kids are smart. They need to start thinking and behaving in such a way on our roads so they arrive home safely."
Earlier on Monday, a 16-year-old boy appeared before court, with tears in his eyes, and was charged with two counts of culpable driving causing death following the crash.
The teenager appeared via audio-visual link in the ACT Children's Court on Monday, having allegedly been behind the wheel of a Toyota sedan when it crashed into a tree in the northbound lanes of the Monaro Highway at Hume on Sunday morning.
Two teenage girls, aged 14 and 15, were found in the vehicle and declared dead at the scene.
Police said two other teenagers were thought to have been involved and to have fled the scene.
After subsequently being found, they received medical attention.
The boy alleged to have been behind the wheel has also been charged with single counts of driving as an unaccompanied learner, and failing to stop and render assistance.
Police allege he was in breach of bail and a good behaviour order.
A Legal Aid duty lawyer did not apply on Monday for the boy to be granted bail, and magistrate Jane Campbell adjourned the matter until October 31.
Detective Acting Inspector Brian Tadic said the impact was "severe".
The northbound lane of the Monaro Highway was closed for most of Sunday.
The crash takes the number of road deaths in the ACT this year to 14, compared with 11 for all of last year.
Police have asked anyone who might have information about the crash to contact them.
"Anyone who witnessed the car leave the road or who drove past the collision site and saw the vehicle prior to 8am on Sunday is urged to contact Crime Stoppers on 1800 333 000, or via the Crime Stoppers ACT website. Please quote P2107669," a police statement said.
"ACT Policing urges all road users to slow down and drive to the conditions."
