The 15-year-old involved in Wednesday's Capital Hill crash remains in a grievous condition at the Canberra Hospital, police say.
He was found "very badly injured and unresponsive" on the road next to an upturned car in the early hours of April 17.
The injured boy was found about five to 10 metres away from a stolen white Toyota Camry which had been almost destroyed in a crash on Adelaide Avenue near State Circle, acting Inspector Mark Richardson said.
Police said the stolen car had been involved in several incidents in which the driver had failed to stop when signalled to do so by police, and in one incident raced away at such excessive speed in a suburban area that police could not pursue it.
However, it remains unclear at this stage of the investigation whether the injured boy was the sole occupant and driver, or whether someone else was in the smashed car and escaped before emergency crews arrived.
Police are checking hospitals to see if anyone has or will turn up with injuries suggesting they were in a crash.
"There is potential that the person was a driver and was unrestrained, was a passenger and was unrestrained or managed to get themselves out of the vehicle," Mr Richardson said.
"Given the person was outside of the vehicle, it's difficult to say with 100 per cent certainty that they were the sole [person]."
Mr Richardson said he believed members of the public came across the accident and called emergency services.
The teenager was breaching bail conditions and unlicensed, the officer said. The bail conditions were related to similar alleged offending.
The severity of the crash - which caused "catastrophic" damage to the car - suggested it was speeding, Mr Richardson said.
"The vehicle was absolutely destroyed," he said.
"This is an unlicensed driver, so there's clearly inexperience factors involved as well if that person is found to be the driver."
Inspector Richardson said he did not know if the injured boy was involved in any of those previous fail-to-stop incidents. The teenager's identity has not been revealed.
Northbound lanes on Adelaide Avenue, heading towards the city, were closed for much of Wednesday for crash investigations.
Road users were advised to turn off before The Lodge, near Empire Circuit. Police were diverting traffic while southbound lanes remained open.
Two people have died on ACT roads this year so far.
Tennis coach Alicia Celaya Jauregui died after riding her bike on Lady Denman Drive in late March.
A 19-year-old died after a collision allegedly involving an underage driver in January.
A man is also in a serious condition after a collision with a car on Good Friday near the Prime Minister's house, The Lodge.
