Assistant police inspector S V Pawar of Mumbra police station said that both Abdul Khalid Mohamad Kausar, the accused, and the victim's family hailed from Darbhanga in Bihar.
Kausar and the girl's father worked as jari workers in Mumbai and lived together in Kausa area of Mumbra.
Last night, at about 9, the victim's parents left her and her five years old elder sister in Kausar's care and went to the market. When then returned after an hour, they found that their younger daughter was bleeding and lying unconscious, while Kausar was nowhere to be seen.