A statement from Thames Valley Police (TVP) on the third anniversary of the disaster said 870 tonnes of evidence are being forensically analysed at the site in Buxton, Derbyshire.
In addition, manslaughter charges and offences under the Health and Safety at Work Act are still being investigated.
Four men died on 23 February 2016 when part of the boiler house at the disused power station in Oxfordshire gave way during demolition work.
TVP assistant chief constable Jason Hogg said TVP and the HSE “remain committed to obtaining answers and justice for those who have been affected”.
He added: “A team of experts from HSE and Thames Valley Police, supported by independent scientific experts, continue to analyse thousands of exhibits and work through complex technical data which takes significant time to analyse and interpret.
“Further detailed interviews of both witnesses and potential suspects are also planned to further progress the investigation.
“Due to the complexity of the investigation we are working closely with the Crown Prosecution Service to make sure that all appropriate lines of enquiry are fully explored.”
Sarah Jardine, head of operations at the HSE’s construction division, said the regulator was “working tirelessly” alongside the police and remained “committed to getting to the truth of what happened for the families”.
“The investigation will reveal if any criminal offences have been committed and it seeks to learn any wider lessons for the industry to help prevent anything like this happening again. More details of our investigation will be shared as and when we are able to do so,” she said.
The four victims – Michael Collings, Ken Cresswell, Christopher Huxtable and John Shaw – were employed by Coleman and Company, the demolition contractor responsible for decommissioning the site when the structure came down.
IOSH Magazine reported last year that Coleman and Company said its own investigations “clearly show” how the accident happened.
After a pre-inquest hearing at Oxford Coroner’s Court in January 2018 the firm’s director James Howard said: “We commissioned our own investigations which, in our view, clearly show why and how units one and two of the boiler house collapsed. We believe the findings highlight industry-wide practices that need to be challenged and reviewed.
“We now consider it essential to share this learning as a matter of urgency, so that immediate steps can be taken within the industry to prevent future loss of life and so that the families can begin to understand what caused this dreadful accident.”