A 59-year-old Hong Kong woman was arrested for allegedly gouging out her elder sister’s eye in a flat in Causeway Bay on Hong Kong on Tuesday.

She was arrested and charged with assault, but her motive was unknown, Oriental Daily reported. The incident happened at 3 am when the sisters’ neighbor called police after hearing screams for help coming from the apartment in Kanfield Mansion in Tai Hang.

The woman had been sleeping in the living room when the attack happened. The middle sister heard the screams and ran out of the bedroom to stop the youngest sister’s attack. When police arrived, they found the oldest sister, aged 66, with her left eye pulled out.

Paramedics sent the victim to Ruttonjee Hospital in Wan Chai and later transferred her to Pamela Youde Nethersole Eastern Hospital for surgery. The suspect was also sent to a hospital for a checkup.

After an initial investigation, police classed the case as wounding and the crime investigation unit was following up. It was understood that three sisters lived in the apartment since 2005. Their parents passed away many years ago, Apple Daily reported.

The oldest sister was wheelchair-bound as had been suffering a spinal illness. The youngest sister was mentally disabled, but there was no record of her illness. The middle sister, a clerk, took care of her sisters without other people’s help.