The police still have a complex task ahead of them in proving criminal liability in the CTV building collapse.

Four search warrants were executed over the weekend, in which documents and other items of interest were seized.

Nigel Hampton QC, who represents one of the widowers, believes it's positive for the families but the process is still complex "in terms of passage of time and intervening events between the first design of the building and it's ultimate collapse."

Its understood Engenium Consulting in Christchruch, which was formally connected to Alan Reay, was one of the premises targeted.

Nigel Hampton QC said there would need to be a "specific and defined" reason for police to search the premises, and they would have needed to show cause to a District Court Judge to get sign off.

"You can't get just a general warrant saying go along and uplift anything in the offices that might relate to a particular thing," Hampton said.

115 people died in the collapse of the CTV building, more than half of the total fatalities of the 2011 Christchurch Earthquake.

Police announced that they would be advancing a criminal investigation in September last year. As yet, charges have not been laid in the investigation.