The incident took place near Elathur in Kozhikode district.
A joint team of central intelligence and anti-terrorism officers arrested a suspect on Wednesday in connection with a train fire that killed three people and injured several others in Kerala on Sunday night, officials said.
The suspect, identified as Shahrukh, was caught in Ratnagiri district in Maharashtra, about 1,000 kilometres north of Kerala after a sketch of him was circulated by the Kerala police based on a witness's account.
"A team of Kerala police has also reached Ratnagiri and the accused will be handed over to them soon," said an official of the Maharashtra Anti-Terrorism Squad, who spoke on condition of anonymity because he was not authorized to talk to the media.
The motive behind the attack was not clear yet, but the official said the suspect had confessed to setting fire to a passenger after an argument on board the Alappuzha-Kannur Executive Express train near Elathur in Kozhikode district.
The suspect had poured petrol on a passenger and set him ablaze inside the D1 compartment of the train around 9:30 pm on Sunday, creating panic among the passengers and triggering a stampede. The fire quickly spread to other seats and luggage, engulfing the coach in flames.
Three people died on the spot, and several others sustained burn injuries. Five of them were admitted to Kozhikode Medical College and three to a nearby private hospital. At least three of the injured were women.
The train was stopped at Elathur station and the fire was doused by railway staff and local residents. The affected coach was detached from the rest of the train and taken to Kannur station for further investigation.
The National Investigation Agency (NIA), which probes terrorism-related cases in India, inspected the train coaches at Kannur station on Tuesday and collected forensic evidence. The NIA also questioned some of the passengers and railway staff who were present at the time of the incident.
The Kerala police had formed a special team to probe the case and announced a reward of Rs 2 lakh for any information leading to the arrest of the suspect. The police had also released a sketch of the suspect based on the description given by Razak, a crucial witness who escaped with minor injuries.
The sketch showed a man with a beard and a cap, wearing a dark-coloured shirt and trousers. The police had appealed to the public to share any information about his whereabouts or movements.