Murtza Chaudhry, aged 21, Arbaaz Hussain also aged 21, Zeeshan Khalid, aged 20 and Tayyab Siddique, aged 22 all died in the incident which happened at around 5.30am on 2 August.
All the men were from the local Bradford area. The post mortems have now been held.
-> Four friends died in horrific high speed crash after police pursuit in YorkshireA statement from the The Independent Office for Police Conduct (IOPC) said: "We understand at this time that the grey BMW 1 Series car in which they were travelling was pursued for a short time, by an unmarked West Yorkshire Police car, due to excessive speed before the crash.
"All four men died at the scene. Their families have been informed and family liaison staff from the IOPC are supporting the families involved.
"We are aware that there is some concern that the police vehicle made contact with the BMW prior to the crash.
"Having reviewed some of the evidence already, we can confirm there is no indication of this.
"We can also confirm that time between the police car first having sight of the BMW and the collision with the tree is approximately one minute according to the evidence we have analysed so far.
-> VIDEO: Footage from scene of Bradford crash where four men died shows car wreckage"Our investigation will focus on the circumstances of the pursuit and the actions of the officers involved, who are all being treated as witnesses.
"Anyone who witnessed, or recorded, the incident is asked to contact us on 0800 096 9079 or email [email protected]"
IOPC Regional Director Miranda Biddle: “We have support in place for the families of those who have died. We have met with them to discuss our investigation and we will continue to update them about our work. My thoughts are with them, and all those affected by this incident including all emergency services involved.
“Our investigators attended the post mortems for the men who died. Both of the vehicles involved were removed from the scene and secured; a process overseen by our investigators. Both are now being forensically tested. This is a fast-moving investigation, and we have already conducted house to house enquiries and collated independent evidence including footage from the police car and local CCTV.
“Footage of the incident, and the aftermath, from what appears to private CCTV has been shared in the media and on social media. I would ask that this be removed to avoid any further distress to the men’s families and those involved and instead is shared with our investigators, using the witness appeal phone line or email, so it can be examined as part of our investigation.
“I would like to ask for the privacy of the families to be respected at this most difficult time.”