The "very complex" criminal investigation into the deadly collapse of the Canterbury Television building in the February 2011 earthquake is still ongoing, with no decision yet on whether anyone will be charged.
Investigators have interviewed more than 100 witnesses and raided the offices of Engenium Consulting Engineers, formerly Alan Reay Consultants, which designed the ill-fated Christchurch office block in the mid-1980s.
Today, police said engineering consultants Beca were continuing to provide expert opinions to the inquiry team.
And it's also been revealed the engineers are now making replicas of the structure to test its critical elements.
"It remains a very complex investigation and a number of key areas need to be finalised before any assessment of liability can be discussed and advanced," Detective Superintendent Peter Read said.
The inquiry team has also engaged the services of a further consultant engineer as well as a solicitor.
While Mr Read said the probe's progress "has considerably advanced", he would not put a timeframe on when any final decision will be made other than "we are working towards a goal" of late 2015.
The victim's families have been advised today on the progress of the investigation.
"Police will continue to keep them informed as we work through this very complex enquiry," Mr Read said.
The six-storey concrete CTV Building pancaked in the vicious magnitude 6.3 February 22, 2011 quake, claiming 115 lives.
In 2012, the royal commission of inquiry found serious errors by engineers, structural designers and the Christchurch City Council.
After the report's release, families and friends of the victims called for legal action to be taken against those responsible.
The commission said Dr Reay should have recognised that his employee David Harding was working beyond his limits when designing the building in 1986.