He allegedly strangled nine-year-old Eman Tanvir at their grandmother's house in Shalimar area in Lahore last week. The Shalimar police said they have arrested Abdul Rehman four days ago, the Dawn reported.
A case of murder has been registered against unidentified killer(s).
Earlier, the police had taken victim's step-mother Saba into custody for interrogation but later released her. The minor girl was killed by her elder brother over "jealousy", Civil Lines Division Superintendent of Police (SP) Investigation wing Hasnain Haider said.
Mr Haider said the boy later cut a vein of his arm and also locked the door of the room from inside to hide his crime. When the grandmother returned, she found the room locked. She called the neighbours for help. The neighbours broke open the door to find the girl to be dead and her brother with an injury on his arm, the report said.
During interrogation, the boy said that he used to watch a TV show from where he had got the idea of killing his sister. CID is an Indian detective television series in which different crime cases are investigated.