A police official told IANS that they are hoping to get information from the public about the bald man who was seen in a camera footage running away from the train minutes before the two bombs went off.
The blasts in S4 and S5 coaches killed one young woman and injured 14 people.
On Friday, Inspector General of Police in Crime Branch-Criminal Investigation Department (CBCID) Maheshkumar Aggarwal said: "We found the movements of a bald person getting down from the S3 coach and running away as unusual from the CCTV footage. His movements were unusual."
The blasts in S4 and S5 coaches killed one young woman and injured 14 people
Aggarwal stressed the police does not consider the man as a suspect in the case but sought his presence in the investigation to explain his unusual movements.
He said the man got off the train at 7.08 a.m. The two bombs went off in succession at around 7.15 a.m.
According to Aggarwal, the man was not seen getting on the train at the Chennai Central station but was only seen getting down and running away.
The police officer said the investigating team is also checking the camera footage at all other stations between Bangalore and Chennai Central stations.
A senior railway police official told IANS that security at the railway station has been beefed up without inconveniencing the travellers.