Police won't prosecute over CTV building earthquake collapse

Police have announced they will not prosecute over the collapse of the CTV building during the 2011 Christchurch earthquakes.

The office block pancaked in the February 22 quake, killing 115 people.

"After very careful consideration of all the information available to us, including the legal advice and expert opinion, Police has determined that there will be no prosecution arising from our investigation," a spokesperson says.

"We fully recognise that there will be disappointment with this decision."

A Royal Commission of Inquiry found flaws in the building's design and construction, but nobody has yet been held responsible.

Police started a criminal inquiry in September 2014. A legal review by Crown Law was completed, following an earlier review by the Christchurch Crown Solicitor.

Critical elements of the building's structure were physically re-built and tested as part of the investigation, along with specialist engineers examining the site and foundations.

"The investigation did identify significant deficiencies in the CTV building design, and Police considered charges of negligent manslaughter," the spokesperson says.

"However we concluded that the evidence available was not sufficient to provide a reasonable prospect of conviction in court, as is required under the Solicitor General's prosecution guidelines.

"Furthermore, technical legal obstacles were identified regarding the length of time between the conduct of individuals and when the deaths occurred."

Families were informed of the decision not to prosecute in a letter on Thursday.