The body of the victim, whose identity is yet to be established, was found with bite marks all over his body, including his throat and private parts, on a passenger train that had just arrived from Erode at the Jollarpet railway yard after dropping passengers at the station, police said.
Some local people, who saw the incident, caught hold of the assailant, estimated to be in his mid-20s, and handed him over to the police.
Asked what triggered the "biting spree," he said they were yet to ascertain it. "The man who bit his victim appears to be mentally challenged. He is incoherent. Probe is continuing."
The train was parked at the railway yard for regular maintenance work before the next trip. The yard is located amid deserted open grounds. A ticket from Chennai from Erode was found on the person of the victim, the Inspector said.
"It is not known if the victim and the alleged killer actually travelled by the passenger train or as to how they reached the train in the yard," he added.