Unnao, May 11 (IANS): Police in Uttar Pradesh's Unnao have detained four family members of a deceased girl in a case related to honour killing.

The girl and her boyfriend were found hanging from a tree on Wednesday over allegations that the two were murdered because they were in a relationship and belonged to different castes.

Both the girl and boy were 17 years old.

The local police initially treated the crime as a suicide pact, but changed their line of investigation after autopsies found the girl had been strangulated and the boy's body bore signs of multiple injuries, including a broken neck which was the cause of death.

Unnao Superintendent of Police (SP) Siddharth Meena said: "We have registered a case of murder and under the Scheduled Caste and Scheduled Tribe (Prevention of Atrocities) Act against seven people. Those behind the incident will soon be arrested."

According to police officials, the seven people -- all related to the girl -- named in the FIR are absconding.

Four family members have been detained.

The officials said that the girl's family opposed the marriage since they belonged to an upper caste and the boy was a Scheduled Caste member.

Opposing their relationship, the girl's family lodged an FIR for kidnapping against the boy on March 7 when the two eloped.

Both were found by the police and the boy was sent to a juvenile home on charges of kidnapping in March.

The girl, however, denied being kidnapped by the boy following which the latter was released in May.

SP Meena said the police are investigating the case and the remaining accused persons would be arrested soon.