Surfers Paradise man Gable Tostee has been arrested over the death of New Zealand tourist Warriena Wright, who fell from the balcony of his high-rise apartment last week.
Mr Tostee reportedly met Ms Wright through an online dating app while she visited the Gold Coast for a close friend's wedding.
The 28-year-old is being questioned by police but has not been charged.
"A 28-year-old man is currently assisting police with their enquiries into the sudden death of a 26-year-old woman at Surfers Paradise high-rise apartment complex on August 8," police said in a statement.
In recent days, Mr Tostee declared his innocence on Facebook and a body building website.
Ms Wright fell from the 14th floor of Mr Tostee's Avalon apartment at Surfers Paradise shortly after neighbours reported a disturbance inside.
Her mother and sister flew into the Gold Coast this week to help police with their investigation.
Ms Wright's younger sister Reza, 23, made an emotional plea for information from the public.
Through tears, she said it was hard to start the grieving process when mystery still surrounds her sister's death.
"It is hard for me facing the loss of my sister without knowing what happened in the last hours of her life," she said.
The sisters, who had lived briefly in Australia when they were younger, had a tight bond and Ms Wright often took on a parental role.