Eight people were crammed into the five-seater family car at the centre of Saturday's horror crash which killed four and left five more fighting for their lives.

Mourners at the scene of the crashThe party of eight were driving along Oxford's Eastern Bypass to the Longwall pub for a meal after celebrating passenger Anton Dublin's 13th birthday at a paintball event in Maidenhead.

Police, who have set up a team of 25 officers, today began an investigation into why the car lost control and careered across the central reservation into oncoming traffic.

Schoolboys Marshall Haynes, of Headington, Liam Hastings, of Rose Hill, and Josh Bartlett, of Blackbird Leys, all aged 13, died, when the Citroen Xsara hatchback they were travelling in crashed at 7.35pm on Saturday.

Anton and three other friends enjoying his 13th birthday party, Connor Hunt, Aiden Wood and Jake Draper, were left fighting for their lives at John Radcliffe Hospital, Oxford.

It is believed both Anton and Connor have been showing signs of improvement but are still on the critical list.

The driver of the car was Anton's mother, Angela Dublin, a 45-year-old former nurse at the JR, who is in a critical condition at Swindon's Great Western Hospital with neck and head injuries.

Police revealed she will be interviewed on the cause of the crash when she recovers.

The crash also claimed the life of Howard Hillsdon, of Yarnton, who was driving his Honda Civic in the opposite lane.

Speaking at the crash site yesterday, police revealed that investigations will centre on the lack of a crash barrier, whether there were too many people in the car and if the boys were wearing seatbelts.

Insp Steve Bridges said: "We are still trying to establish why the Citroen Xsara left the road and crossed the central reservation.

"At this stage we are keeping an open mind about the cause of the crash.

"When she (Ms Dublin) wakes up, we will be able to ask her version of what's happened here.

"The most important thing for us is to piece together what happened to help the grieving process for the families.

"We obviously know how many people were in that particular car, the Citroen, that's one aspect that we will be looking into, but in terms of any actual prosecution, it's much too early to say.

"I would speak for all emergency services when I say it was a very tragic incident, one of the worst ones I've seen in some 23 years and the problem is it involves young people. It was a devastating incident and inquiries are now 48 hours long and we can only now start making moves to find out what happened."

Insp Bridges revealed the section of the road where the accident occurred is the only part of the ring road without a crash barrier and police will be urging for one to be installed.

A male passenger from the Honda Civic was taken to Stoke Mandeville Hospital, in Aylesbury, where his condition was said to be not life threatening.

A further two vehicles travelling northbound were involved after the initial collision.

The male drivers of an Audi and a Volkswagen were both treated for minor injuries at the scene and at The Horton Hospital, Banbury.

A motorcyclist who swerved to avoid the collision suffered minor injuries and the driver of a VW Polo was unhurt after his car was hit by flying debris.

A team of 15 police officers and 10 family liaison officers are currently dealing with the crash.

All the vehicles were being examined today by investigators and officers were also taking statements from witnesses.

Anyone who witnessed the crash or has any information that could assist officers with inquiries should contact the Roads Policing Department incident room on 08458 505505 or Crimestoppers on 0800 555111.