Four-year old Nusrat Jahan Mim, whose body was found in a bathroom at Karail slum in Dhaka yesterday, was killed by her elder brother, Rab said.
He strangled her "out of jealousy" while she was sleeping, as he felt his sister is loved more by their parents, the 14-year-old told Rab, assistant director of Rab-1 Md Kamruzzaman said.
A team of Rab-1 arrested him from the slum, he added.
During primary questioning, the fifth grader at a local school, told Rab that he thought his parents' love for him started to wane after his sister was born.
The boy used to think that his parents became indifferent towards him. He claimed that his father often beat him up without any reason, and his parents used to entertain the wishes of his sister, Rab said.
He blamed Mim for everything and the resentment grew over the years. Yesterday, when he found his father Liton, a fruit vendor, and mother Ruksana Akter, a part-time house help, not at home and Mim was sleeping, he choked her to death, the Rab official said.
The boy first put the body under their bed but later moved the corpse to the bathroom when everyone was looking for Mim, the Rab official said.
An autopsy at Dhaka Medical College Hospital morgue primarily found that the child was choked to death.