Xu Dayuan stared at Zhou Ning, his lips pursed for a long time before he said:
"I didn't tell you just now because after the interrogation yesterday, Zhu Xingmin confessed some information that we've been unable to verify as true or false. He said he has a twin brother, an undercover operative like himself but more successful and better trained.
He's always either going to Las Vegas or vacationing on islands, only reaching out to his brother when he needs his identity, tossing him some cash symbolically as one would treat a bar girl, claiming that this person is a core member of the northern region.
Mr. Hu has not been able to verify his account, as we have limited information on the core members of their northern region. According to your analysis, Zhu Xingmin wasn't lying, and this killer could very well be his twin brother.