The deceased were identified as Suraj (21), Keshav Prasad (48), and the bus driver, Wajid (48), who died of a cardiac arrest, said police.
The incident was reported around 3.20 PM, when the orange cluster bus - on 419 route - lost balance and ended up hitting a mini-truck and a three-wheeler, near the Kotwali police station and then hitting five persons.
"The members of the committee inspected the spot where the incident took place and have submitted its preliminary report. The committee has also been asked to submit its final report within 72 hours," said a senior government official.
According to the police, while Prasad died on spot, after being crushed between two vehicles, the others - including the driver - were declared dead when rushed to a hospital. When an agitated crowd approached the driver after the accident, they found that he was sitting motionless in a slightly twisted position on his seat.
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Presently, two persons are admitted at Sushruta Trauma Centre and one at Lok Nayak Hospital, and all three of them are reported to be critical, said the senior official.
"We have registered a case under Sections 279 (rash driving) and 304A (causing death by negligence) of IPC . Further investigation is underway," said DCP (North) Madhur Verma.
Preliminary investigation suggests that the driver had a cardiac arrest while he was on wheels, which led the accident. However, no conclusions can be drawn unless the post-mortem report is obtained, Verma said.