A BNP leader and his sister were arrested in Rangpur city on Tuesday on charge of killing a domestic help.
The arrestees are Kawsar Zaman Babla, vice president of Rangpur city unit of BNP and his sister Laboni Akter.
Police also picked up two more persons with them.
Police arrested them from Mahiganj and Munshipara areas of the city on Tuesday night, said Rezaul Karim, officer-in-charge of Kotwali Police Station.
Sumi Akter 14, of the city, worked at the house of Babla's sister Laboni as domestic help. On Friday, the accused killed the girl and buried her secretly.
Following a case filed by the victim's mother, police arrested them on Tuesday night.
Babla contested in the Rangpur City Corporation election for mayoral post with BNP ticket last year.