UPDATED 5.21pm: Police say they wanted to bring charges over the collapse of Christchurch's CTV building during the February 2011 earthquake, but just didn't have enough evidence.

"We are disappointed we couldn't satisfy the wants and needs of the families, but we have to measure the evidence we had," Detective Superintendent Peter Read told reporters on Thursday after advising the victims' families no charges would be laid over the disaster.

"If we had taken my heart's advice we would've prosecuted."

The decision not to lay charges comes after a $1.18 million criminal investigation which began in August, 2014.

"All the legal opinions and police recommendation was that we were unlikely to get a conviction," Det Supt Read said.

Police investigated potential charges of negligent manslaughter against engineers Alan Reay and David Harding, who were responsible for the CTV building's design in the 1980s.

An engineering report in 2014 identified a number of significant deficiencies in the building's design.

"The prosecution must also prove that the defendant's negligence caused the death of the individuals concerned," Deputy Solicitor-General Brendan Horsley said.

But there was also a technical obstacle to the prosecution in the case, as the Crimes Act required death to have taken place within a "year and a day" after negligent conduct ceased, he said.

Law reform is currently being considered for the "year and a day" rule.

While some families have expressed disappointment with the announcement, Maurice Gardiner, who lost his sister Donna Manning in the collapse, says he is at peace with the decision.

"Our family has always said that because of the horrific way our loved one passed away, that we didn't want to have a witch hunt," Mr Gardiner told NZ Newswire.

"That was our stance from the start, and it is still is."

He said nothing would bring his sister back, and that prosecuting someone would not make the family feel any better.

The six-storey building collapsed and caught fire after the magnitude 6.3 quake struck on February 22, killing 115 people inside, including 65 foreign students.

Police will speak with victims' families next month, including affected families in Tokyo.

CTV building collapse: a timeline

* 1986: Permit issued for CTV Building in Christchurch.
* 1991: Steel bars installed to deal with connection issues.
* 1987: Report identifies "a vital area of non-compliance in the connection of the floors to the north wall complex".
* 1991: Steel bars installed to deal with connection issues.
* 2008: Kings Language School leases the fourth floor of the building.
* Dec 27, 2010: After the city is shaken by an earthquake, the CTV building is again inspected and given a green sticker.
* Feb 22, 2011: the six-storey building crumples and catches fire within seconds of a major earthquake, killing 115 people, including 64 foreign students.
* 2012: The CTV building's collapse is one of several investigated by the Canterbury Earthquakes Royal Commission.
* 2014: Subsequent investigations revealed the building was not built to standards of the time and police begin looking at criminal charges.
* Dec 16, 2016: Police complete their report.
* Nov 30, 2017: Police announce they will not prosecute anyone for the building's collapse.