The accused, Sanjay (22), is a school dropout. He used to work in a nail polish factory, police said, adding that he had five siblings and his father owned a 'chaat' cart.
He was arrested today from the Sawan Park slums.
"Was highly concerned about the assault case on our media friend Ms Kalra. I congratulate NW Distt team for quickly solving this blind case (sic)," tweeted Delhi Police Commissioner Amulya Patnaik.
The accused was identified after questioning various people, including the regular visitors to the park, said DCP (Northwest) Milind Mahadeo Dumbere.
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Police began rounding up the rogue elements, drug addicts and those who had previous criminal records in the area. Some of those detained told the police about the presence of the accused at the park at the time of the incident.
"He confessed that he had seen Kalra at the park around 8-10 times and was infatuated with her. He accosted Kalra to talk to him, with a view to befriend her, but in vain. In a fit of rage, he attacked her with a stone," said another officer.
As Kalra raised an alarm, the accused fled.
He was neither aware of the fate of the journalist nor of the subsequent uproar the incident had created, police said.
Meanwhile, the police said Kalra was recovering and showing signs of improvement.
The incident has brought the issue of women's safety back to focus in the national capital and Delhi Police has come under attack from various quarters, including the Delhi Commission For Women, for not doing enough to curb crimes against women.
However, the police sought to assuage these concerns.
"Women's safety is our utmost priority. With our newly launched Prahari scheme, under which the security guards will be trained by the police to act as informers, we aim to address the issue more effectively," said DCP (Crime) Madhur Verma, who is also the PRO of Delhi Police.