The Philippine committee investigating last month's deadly hostage-taking will travel to Hong Kong to interview survivors.
The Incident Investigation and Review Committee also said it needs more time to finish its initial inquiry into the August 23 tragedy in Manila, in which eight Hongkongers lost their lives.
The news came as the director-general of the country's police force, Jesus Versoza, said he is going into early retirement while assuming full responsibility for his men's blunders in the botched rescue attempt.
The committee was to finish its inquiry today, but its chairwoman, Justice Secretary Leila de Lima, said it will be extended until Wednesday.
A Hong Kong police spokesman said a request has been received to assist in the visit by the Philippine committee - which will take place after its initial inquiry is complete.
With the consent of survivors, police will provide copies of witness statements and arrange for meetings. Assistance with ballistic examinations will also be provided.
The spokesman also said several mobile phones turned over to Hong Kong investigators do not belong to SAR residents and that the Philippine authorities have been notified.
Manila acknowledged at the weekend that one of the phones used by the hostage-taker had been mistakenly turned over to Hong Kong police. The gunman, dismissed police officer Rolando Mendoza, was killed in the shoot-out that brought the standoff to its bloody end.
The Philippine committee is questioning various government and police officials to find out who is responsible for the bloody outcome of the crisis.
Members of the inquiry board will inspect the scene of the hostage-taking off Rizal Park tomorrow. And a reenactment of the 11-hour crisis will be carried out on Wednesday at a police camp where the bullet-riddled bus is stationed, de Lima said.
Philippine National Police chief Versoza yesterday said: "I take responsibility for all PNP units and all police personnel in everything they did or failed to do.
"More than ever, it is imperative to take responsibility especially with regard to what has transpired in the past week."
He told the inquiry earlier that he left town at the height of the crisis on official business.