Police sources said that they have got the information from the investigating team and picked him up from his house in Tirunelveli.
He was arrested on Friday mid-night, said the Chennai City Police Commissioner T K Rajendran.
"When the Police arrived he tried to cut his throat with a blade. He was immediately taken to hospital and is under treatment. He is fine and would recover, though he is not fit to travel now," Rajendran said .
He added that the crime is one of stray incident in which a youth, who was infatuated with the girl. He wanted to move with Swathi which was not successful. Hence, he killed her.
Ramkumar did not have any accomplices in the crime, he said refuting collaboration theory speculated by a section of the media.
When media questioned on increasing day light murders and hackings in the city in the recent months, the City Police Chief said that there were stray incidents that had no correlation to the law and order in the city or in the state. In all cases, the culprits were arrested promptly and cases filed.
Ramkumar, is an unemployed engineering graduate and has two sisters. His father is a BSNL employee and mother a housewife.
News agency IANS has quoted an official by saying: "It seems the family is unaware of his alleged deed."
He said that Rajkumar's neighbours were reluctant to speak about the youth after coming to know the reason behind the police action and the motive of the killing was being investigated
Ramkumar, was staying near victim Swathi's residence in Choolaimedu area here. He had stalked her for months before allegedly murdering her by using a sickle at the Nungambakkam railway station around 6.30 am on June 24 while waiting to board a train to her work place.
Pulling up the police for leaving her body for nearly two hours on the platform, the Madras High Court had warned of suo motu intervention if there was slackness in the probe.
The case was transferred from railway police to the city police, which formed several special teams for the probe headed by an assistant commissioner.
With no CCTV camera in the railway station, police faced a tough job in obtaining clues and managed to get visuals of a man, suspected to be the assailant, from a CCTV installed at a house in the neighbourhood. They had also released the footage and also a sketch of the suspect.