The Bar Association on Monday deplored "in the strongest possible terms" acts of arson at two court buildings on Sunday, while a deputy director of the Basic Law Committee, Maria Tam, called for the immediate arrest of the culprits.
In a statement, the association said people who commit such acts are not genuine protesters but criminals, and they must be brought to justice.
The association's chairman, Philip Dykes, said the acts cannot be defended or justified in any manner.
"I can't speculate upon the motives of the people who took fire to the Court of Final Appeal and the High Court. I don't know what motivated them. If they're frustrated with the way that the system seems to be working, they [should] express that frustration in other ways than attacking the courts," Dykes told RTHK's Damon Pang.
"Even though it is minor, minor damage caused by fire, it is nonetheless significant, cos no justification can be found for that at all. It's an assault against an institution which symbolises the rule of law and the protection of rights and freedoms."
Meanwhile Tam, who is a top member of the Basic Law Committee, called on police to arrest those who set the fires.
She said the "rioters" responsible had been extremely disrespectful to the SAR's rule of law.
Tam said the majority of people are sick and tired of the use of violence in the city, and this is the best time to return to rational discussion.
But when asked if there's any concessions the government could make, Tam said that's up to Chief Executive Carrie Lam to decide.