The bus plunged 50 metres off the bridge into the Yangtze, China's longest river, in Chongqing city on Sunday.
Before Friday's statement from the police, footage showed the bus driving on the wrong side of the road before crashing into the water.
CCTV from on-board the bus shows how a passenger appeared to lash out at the driver, who in turn retaliated, seconds before the bus crashed and plunged into the Yangtze River.
According to the China Daily, a female passenger named Liu had missed her stop and asked the driver to stop immediately.
The surveillance recording showed that at 10.03am, five minutes before the accident, the woman stood up from her seat, walked up to driver and began cursing him.
The woman then used her mobile phone to strike the driver's shoulder, while the driver used his right hand to stop her attack and restrain her.More news: Statue of Unity Interesting facts about the world s tallest statue
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Dashcam footage from an oncoming vehicle then shows the bus veering off its lane, colliding with a auto and smashing through a bridge guardrail before plunging into the river.
According to the Ministry of Emergency Management, the salvage work was especially hard because of the small size of the bus, the depth of the water, limited visibility and shifting currents that impeded divers.
Salvage teams deployed 70 rescue boats, three floating cranes and eighteen divers to recover the bodies of 13 passengers. Fifteen people were on board the bus at the time.
Authorities ultimately blamed the 42-year-old bus driver for not following safety protocols but found that both the passenger and the driver had broken the law and endangered public safety.
As the quarrel escalated, the statement said, the woman hit the driver on the head with her cellphone.