HONG KONG (UPDATE) - Hong Kong police will study bullets test fired from guns used by a Manila hostage taker in an incident that left 8 of the city's tourists dead, reports said Friday.

The incident, which strained relations between Hong Kong and Manila, has raised questions about whether the tourists were killed by a lone gunman -- disgruntled ex-cop Rolando Mendoza -- or by police during their botched rescue operation on August 23.

Mendoza was shot dead by Philippine police, ending a 12-hour standoff drama played out on live television around the world.

Two police officers from Hong Kong on Thursday brought back spent shells after test firing Mendoza's weapons, an M16 assault rifle and .45 caliber pistol, the city's media reported.

The officers were held up at the airport in Manila on Thursday on doubts over whether they had clearance to take the bullets and casings out of the country.

"Mr Li Kwai-wah, chief inspector from Hong Kong, was actually authorized to bring those shells with him to Hong Kong. They have a clearance from the Philippine National Police," Philippine Justice Undersecretary Jose Vicente Salazar said Thursday.

"It was just that, at this time, all those items related to the (bus hijack) investigation being brought out must be cleared by the Department of Justice."

Salazar added that the police officers were later granted clearance to take the bullets to Hong Kong.

"In fact the (Chinese) police attache admitted that they failed to obtain (justice department) clearance," he said.

Police in the Chinese territory declined to say why the bullets and casings had been brought back to Hong Kong or discuss their probe.

"(We) are now actively investigating the case. Since the police will prepare and submit a death report to the coroner, it is not appropriate for the police to release any detailed information about the investigation to the media at this stage," they said in a statement.

Philippine authorities admitted to a string of blunders in handling the crisis, which has dented the reputation of a country in need of the money tourists bring in.

Philippine authorities said they expected to wrap up their inquiry on Monday.