A constable was killed and two of his colleagues were critically injured in the Hastings area late on Monday when an SUV dashed against them.
None of them was wearing a helmet.
Police said the three ' Mantu Kumar Das, 32, Gouranga Mondal, 32, and police driver Prabal Kumar Chaki, 46 ' were found slumped on the ground at the intersection of DL Khan Road and Bejoy Bose Road, where the accident occurred at 11pm.
The three cops from the state force, posted at North 24-Parganas, mostly suffered head injuries as they were flung off the motorbike. They were taken to SSKM Hospital, where Das, a constable with the district armed police, was declared dead on arrival.
Mondal and Chaki were hospitalised in a critical condition.
The penalty for riding a two-wheeler without a helmet is Rs 100 for the first, second and third offences and Rs 300 for the fourth and subsequent offences.
It is also illegal to carry more than one adult pillion-rider.
"None of the three bike-riders was wearing a helmet, which probably turned the accident fatal. They received mostly head injuries," said a traffic officer.
The Mahindra Scorpio that hit them sped away from the spot, only to be intercepted at Ekbalpore. The driver was arrested and the vehicle impounded.
nFreak death: A 17-year-old factory worker was killed when a towel he had kept around his neck got entangled in a machine at a rolling mill in Salkia, Howrah, on Monday. Ravi Ranjan Singh was sucked into the machine and crushed. Ravi's father Kewal Singh claimed the mill owners, Anil Singh and Prem Singh, declared the factory closed after the accident, stuffed the body into a sack and left it on the mill premises before fleeing. Police have slapped a murder charge on the owners.