A teenage girl who was allegedly tied up and thrown into a swamp to drown in an honour killing had infuriated her strict father by refusing to wear an Islamic headscarf and by using social media, Dutch prosecutors have said.

The body of 18-year-old Ryan Al Najjar was found gagged, her hands tied behind her back and her ankles taped together, dumped in a swamp six days after she vanished from the family home in Joure in May last year.

Her brothers, Mohamed, 23, and Muhanad Al Najjar, 25, are now on trial for her murder, while their father, Khaled – accused of ordering the killing – has fled back to Syria.

Read more: Teenage girl ‘tied up and drowned in swamp in honour killing had upset her father by refusing to wear Islamic headscarf and using social media’