The nail bomb was planted by the accused in the wee hours of Saturday morning.
A man was arrested for the act of vandalism and he was being held on a separate charge of arson.
The suspect is absconding.
The man, who has been identified as Rohit Shah, was the first person to be arrested in the bomb blast on a bus in New Delhi on Saturday.
According to the police, he was caught after the accused was caught with a nail bomb on his chest and a handkerchief.
The nail was discovered after a search of the area.
The police also said that the accused has been released on bail.
The victim of the bomb attack was shifted to a hospital in a critical condition.
The incident took place on a crowded bus in the area of Muthu Nagar in the new Delhi district of Thane.
The bus had just left the railway station in the old city and was going to the new one in south Delhi when the bomb exploded.
Police said that there were several people on the bus at the time of the incident.
The accused is abSconding.
Police had arrested the accused on Friday.
A case has been registered under sections 354, 341, 341B and 34 of the IPC.
Police have also registered an FIR under section 144 of the IT Act for causing hurt by mischief.