The victim was 18 years old.
The arrest followed a two-day manhunt.
"Opposition figures that return to the Maldives...we will slit their throats. We will definitely behead them,” said a ruling party supporter.
Videos on Facebook show about 10 young men fighting. Two can be seen brandishing weapons.
The businessman was convicted over the theft of a US$5 million resort lease payment.
The men are accused of trying to bring the Maldivian Democratic Party to power.
The man was charged in February but a court hearing has not been held so far.
Shujau Usman received death threats last year, local media reported.
There were 11 civil cases, two family cases and two criminal one. The remainder were cancelled.
The 20-year-old was attacked by five men in Maafannu.
An MDP office was vandalised and used oil was thrown into PPM meeting halls.
The judicial watchdog lifted the suspension of Judge Ahmed Rasheed.
A very capable team worked on the investigation, the ex-police chief said.
The Bangladeshi embassy was unavailable for comment.
One of the cancelled trials was for ex-president Maumoon Abdul Gayoom.
Aishath Fazna told local media she was resigning for personal reasons.
Naseer believes the president thought too many state resources were being used.
