Mr Bajwa remains under police guard in hospital.
Police had pulled over a black Porsche for alleged speeding, and four officers were in the emergency lane of the Eastern Freeway preparing to impound the car, when a semi-trailer drove into them about 5.40pm on Wednesday.
New recruits Constable Josh Prestney and Constable Glen Humphris were killed alongside senior colleagues Leading Senior Constable Lynette Taylor and Senior Constable Kevin King.
Richard Pusey, 41, the man pulled over for allegedly speeding in a black Porsche with drugs in his system, has been charged with failing to render assistance among other offences.
“We do have some results [from drug and alcohol testing after the crash] and I’ve been asked not to convey those until such time as he has been interviewed. For those operational reasons,” Mr Ashton said.
“There are some longer term results that we still need to get.
“We will get some further information available to the detectives later today on the crash reconstruction stuff so these vehicles these days, with all the GPS and everything else there’s a lot of data held and … they’ll have quite a good reconstruction.
“The mere fact that he is in hospital and we have been unable to get to him doesn’t mean that they have had to sit idle they’ve been able to actually do a lot of work on reconstruction prior to him being available for interview.”
Police have not described the nature of his medical condition, but have said it was not a result of the accident.
The crash is being jointly investigated by the homicide squad and the major crash investigation unit.
“We do have a fully open mind on it, that’s why it’s pretty much a dual investigation,” Victoria Police Deputy Chief Commissioner Shane Patton told radio station 3AW on Thursday.
“We haven’t ruled anything out at this stage, pivotal to that is obviously speaking to the truck driver.”
Mr Patton said the driver remained under police guard because he was suspected of serious offences, including whether he may be charged with culpable driving resulting in the deaths of four people.
“For us, the focus is very much, though, on the driver of this truck.”
Commissioner Ashton and Deputy Commissioner Patton have both rubbished reports of the truck driver being pulled over earlier in the day as rumour.
Mr Bajwa’s Cranbourne home in Melbourne’s outer south-eastern suburbs was raided on Wednesday night.
“What was found there is still the subject of ongoing investigation,” Commissioner Ashton said on Thursday.
A blood sample for drugs and alcohol was taken on Wednesday night.
The truck involved in Wednesday’s crash bore the logo Connect Logistics, a Sydney-based trucking company whose website has shut down in the aftermath of the crash.
Connect Logistics delivers dairy and other refrigerated items, according to its now-closed website. Despite being based in Sydney, old job listings show a truck driver was hired in Melbourne in 2017.
The company and its managing director have not returned phone calls from The Age.
Mr Bajwa’s family has not returned phone calls.
Rachel is a breaking news reporter for The Age.
Anthony is a sports and general news reporter at The Age.