The investigators issued the latest statement amid speculations that the members of the SWAT team and other police officers that took part in the bloody siege were responsible for the death of the hostages.
Ballistics tests showed that the eight victims' wounds were from a high calibre weapon fired inside the bus where they were held for 12 hours last Monday, national police spokesman Senior Superintendent Agrimero Cruz said.
"With a degree of certainty we can say that the victims were shot by Rolando Mendoza," Cruz said, referring to the sacked policeman who hijacked the bus in a bid to win his old job back and was killed in the bloody end to the siege.
"The result of the autopsy showed that all the bullets that hit the victims came from a high powered firearm," he said on DZBB radio.
The hostage-taking incident started when a sacked police officer armed with assault rifle hijacked the tourist bus carrying 25 passengers at the Rizal Park in Manila Monday morning.
The hijacker, later identified as Senior Inspector Rolando Mendoza, demanded that he be reinstated in the police service.
Mendoza, whose brother is also a policeman, was a decorated police officer with more than two decades of service in the police force. He was discharged in 2008 for his alleged involvement in drug-related crimes and extortion, according to police.
A high Hong Kong official has expressed his displeasure on the way the hostage crises was handled by Philippine authorities.
"The way it is handled -- particularly the outcome -- is very disappointing," Hong Kong Chief Executive Donald Tsang told reporters late Monday.
"There were so many people on the bus -- no one came to our rescue. Why?" one Hong Kong survivor, who identified herself as Mrs Leung, said at the scene.
Manila police officials have been under attack by the public both in Hong Kong and the Philippines for mishandling the Manila hostage incident that led to the death of eight Hong Kong tourists and injury to 15 others.