Sammer, who was arrested yesterday, has confessed to his involvement in the crime, they said.
Three persons, including a relative of a BSP MLA, were booked after the 38-year-old woman was allegedly raped and murdered at the mill owned by a the legislator last week.
Sameer said the woman was strangulated to death after being raped, police said.
Police are searching for other accused who are absconding.