假設一個殺人犯o係大陸同香港都殺左一個人,咁佢o係香港畀人捉到,會o係大陸定香港受審??

For HK Resident:
He will put in front of HK Court for court hearing. If convicted, he will sentence in HK. There is no prison transfer regulation/agreement between mainland & HK.

For Mainlander:
He will put in front of HK Court for court hearing. If convicted, he will sentence in HK. After sentence is completed, HK Immigration will repatriate him back to mainland. He will be prosecuted by Mainland authority, and imprisonment, if convicted.

He will go to prison in hong kong and follow the laws in Hong Kong.