The families of six students killed in the Berkeley balcony collapse have been promised that the case will be "thoroughly and exhaustively" investigated.
A new criminal investigation into the tragedy has been launched by Alameda County District-Attorney Nancy O'Malley.
The US construction firm and waterproofing sub-contractor who worked on the balcony will be interviewed as part of the probe, which will determine whether criminal charges or a civil consumer protection action are warranted.
Addressing the families directly, Ms O'Malley said: "Each of you deserve to have this matter thoroughly and exhaustively investigated. We will do so. That is the pledge I make from my office."
The collapsed balcony was now in the custody of the Berkeley Police Department, which, along with other city departments, was co-operating with the district attorney's office, she added.
The Sheriff's Department is also obtaining custody of a second balcony, removed from the floor below the collapse, for a forensic analysis.
The new probe follows a City of Berkeley engineering investigation which found that the eight timber support beams of the fourth-storey balcony failed due to "severe dry rot".
Six students died - five Irish and one Irish-American - while seven were injured when the timber joists failed at 12.41am on June 16 and the 13 students fell to the concrete pavement below.
The City of Berkeley shocked families and San Francisco locals by saying their investigation had concluded with the engineering report released last Tuesday.
The city is now implementing an audit of all such timber-supported balconies and introducing new building codes and safety inspection measures.
However, District-Attorney O'Malley has confirmed her 60-strong office will now review the City of Berkeley report and all other relevant matters.
Both the builder, Segue Construction, and the waterproofing contractor, R Bros Inc, are expected to be interviewed about the balcony's design and construction.
That probe will be assisted by both the City of Berkeley authority and the Berkeley Police Department.