Police in Canterbury have executed four search warrants as part of the investigation into the collapse of Christchurch's CTV Building.
The six-storey office block collapsed during the February 2011 earthquake, killing 115 people.
In September 2014, the police announced they would advance a criminal investigation once they had assessed a large amount of information regarding the collapse.
The police said today that documents and items of interest had been seized under warrants issued since Friday.
They also said they had engaged engineering consultants Beca to provide an expert opinion to the investigation.
Detective Superintendent Peter Read said the investigation involved consideration of a large amount of complex, technical information, which would inform police on recommendations about any criminal liability.
A decision on whether charges will be laid is expected later this year.