Jaringan Melayu Malaysia (JMM) president Azwanddin Hamzah has been arrested by police.
The arrest came a day after Azwanddin threatened to attack a police station if the authorities did not arrest the perpetrators of last month's Seafield Sri Maha Mariamman Temple riots.
Selangor CID chief Fadzil Ahmat said he will be probed under Section 506 of the Penal Code, which deals with criminal intimidation
Fadzil said the Malay-rights activist will also be investigated under Section 504 of the Penal Code for insults to de facto Unity Minister P Waythamoorthy.
Azwanddin had mocked the minister by referring to him by the P-word slur which is offensive to Indians.
Police will seek to remand Azwanddin in court tomorrow morning.
Those convicted under Section 506 of the Penal Code can be jailed up to two years, or fined, or both.
The law also stipulates that for threats to cause death, grievous hurt, or destruction of property by fire, or to cause an offence punishable by death, the jail sentence can be extended to seven years.
Meanwhile, offences under Section 504 of the Penal Code are also punishable with up to two-year jail, a fine, or both.
Yesterday's rally was to demand justice for slain firefighter Muhammad Adib Mohd Kassim who succumbed recently to injuries sustained after reportedly being assaulted by rioters near the temple.
Authorities said that Adib was dragged out from his vehicle by rioters and beaten. He suffered broken ribs and multiple organ failures.
Adib showed a slight improvement during the treatment at the National Heart Centre but his condition worsened and he died on Dec 17.