A teenager who murdered his 12-year-old sister by cutting off her head in a so-called honour killing apparently practised by killing sheep first.

The boy – identified only as M.M. in local media – claimed he murdered the young girl after hearing rumours that she was bringing disrespect to the family name in their hometown of Bandar Abbas, in Iran.

But residents and family say they are mystified as the girl, named Rahil, was far too young and were more interested in dolls and toys than anything else.

Rahil’s aunt said that when the girl’s mutilated body was found, she was so young and innocent that “she still had toy marbles in her pocket.”

The 12-year-old’s decapitated body was found sometime in mid-February.

Her brother, M.M., at first denied the murder, but ultimately admitted to cutting off her head with a knife.

The incident began on a rainy night when M.M. insisted he take Rahil to a tailor to sew her some new clothes at around 10:00pm.

The two hopped on a motorcycle and travelled about 4 miles away from their home.

Then, M.M. suddenly stopped the bike, got off, and beheaded Rahil.

He wrapped up her dead body in a blanket and headed back towards home.

M.M., who also cut one of his wrists in an alleged suicide attempt, stopped at a nearby mosque where he fell unconscious.

He was found by residents the next morning, laying next to his motorcycle, where they also allegedly found drugs, alcohol and cigarettes.

M.M. was rushed to hospital and when asked about his sister, he simply responded with: “May God bless Rahil”.

Shocked relatives said they do not know why M.M. would do such a heinous thing.

Locals said they knew M.M. as a quiet young man, and his school teacher says that he was a quiet boy during his school days.

Many claim the murder was premeditated, with reports surfacing about the boy having practised his ‘knife skills’ by killing a couple of sheep in the past months.

The boy is currently being held at a drug rehabilitation centre.

The investigation is ongoing.