Three passengers were killed and another was seriously injured in an attack by an unidentified co-passenger in a Chennai-bound Bhadrachalam depot RTC bus at Tada in SPS Nellore district in the early hours of Thursday.

The deceased were identified as Ajay Biswas (25) from Malkangiri in Odisha, Niranjan (28) from Kavali and K. Rambabu (30) from Korrapatipalem in Talluru mandal in Prakasam district. Another passenger, Ramesh, from Ongole suffered serious injuries and was admitted to the Sullurpeta Government Hospital.

The motive behind the attack was not yet established as the assailant indiscriminately attacked the passengers who hailed from different places. Police said the murderer wore black trousers and red T-shirt and had a lean and tall physique.

Passengers said they could not see what was happening as it was dark and most of them were asleep. They suspected that one of the two passengers who boarded the bus at Nellore around 1.30 a.m. might be responsible for the attack. The driver stopped the bus on hearing screams from inside the bus and the attacker jumped out of the bus after opening the door and escaped.

Two passengers were found stabbed in their chest while the third one was injured in the throat.