WELLINGTON, June 15 -- Police investigating the collapse of a building that killed 115 people -- most of them young students from Asia -- in the February 2011 Christchurch earthquake have seized documents in four searches, the New Zealand Police announced Monday.

Four search warrants had been executed as part of the criminal investigation into the reasons for the collapse of the six-story CTV building.

Documents and items of interest had been seized, Detective Superintendent Peter Read said in a statement.

The New Zealand Police announced in September last year that they would advance the investigation after assessing a large amount of information.

Police had also engaged the services of an engineering consultancy firm to provide expert opinion to the investigation.

The investigation involved consideration of a large amount of complex, technical information to inform police on recommendations about any criminal liability, said Read.

Any decisions would be subject to legal review before the final outcome of the investigation, which was expected to be known later this year.

In September last year, the police said the expert opinion would include whether there were any serious departures from accepted standards by those involved in the building's design or construction that could amount to gross negligence.

A report by the Canterbury Earthquakes Royal Commission of Inquiry detailed how the CTV building, which was designed in 1986 and completed around 1988, had a "design that was deficient in a number of important respects" and should never have been issued with a construction permit because it failed to comply with building regulations.

The commission also found the building was never properly structurally assessed after being damaged in strong earthquakes on Sept. 4 and Dec. 26, 2010, despite being inspected by three building officials.

Most of the 185 people killed in the 6.3-magnitude quake of February 2011 died in the building when it collapsed and caught fire.

The CTV victims included 64 Asian students studying at an English language school: 17 students from the Chinese mainland, 28 from Japan, 10 from the Philippines, six from Thailand, two from the Republic of Korea, and one from China's Taiwan.

The New Zealand government bought the CTV site in July last year and plans to include it in a mainly residential area on the edge of the city's new central business district.