SYDNEY, AUSTRALIA -- More than 30 years after American Scott Johnson was killed in a gay hate crime in Australia, police said Tuesday they had arrested a man and expected to charge him.

The breakthrough in the cold case comes two months after the victim's family doubled a police reward in the case to AUS$2 million.

The 27-year-old mathematician Johnson's naked body was found at the base of a cliff in the Sydney suburb of Manly in December 1988.

Police at the time ruled his death a suicide, but a coroner found in 2017 that Johnson had been killed in a hate crime, saying gangs of men roamed Sydney at the time searching for gay men to attack.

In 2018, police announced an $1 million reward for information leading to an arrest in the case, which was doubled when Johnson's brother, Steve, matched the amount in March.

Steve, who had long pushed police to investigate his brother's death, said it was "remarkable" the alleged killer had been apprehended almost 32 years later.

"This is a very emotional day. Emotional for me, emotional for my family who ... love Scott dearly," he said in a video statement.

"It's emotional, I'm sure, for the gay community for whom Scott had come to symbolise the many dozens of other gay men who lost their lives in the 1980s and '90s in a world full of anti-gay prejudice and hatred," he said.

Detectives arrested a 49-year-old man in the leafy Sydney suburb of Lane Cove before beginning searches of a nearby home and the site where Johnson's body was discovered.