A case was registered against Rohit (20), who lives in Vaishali Sector-7 area, on a complaint by the father of the 14-year-old girl, police said.
In his complaint lodged yesterday, the father alleged that Rohit, 20, and her daughter were friends.
Recently, he took her to a shopping mall in Indirapuram, where he offered her soft drink mixed with sedatives and made her obscene video, the father alleged.
"After making obscene MMS, Rohit started blackmailing her and threatened to upload the video on Internet. Girl's father told police that Rohit would often call his daughter and threaten her," a senior police officer said.