Struggling is futile; the man deemed. It was useless, his binds were tightly secured. And under these people's watchful gazes, he doubt they'll allow him to have even a slight bit of chance to loosen it for his convenience.
But the doctor did removed the thankfully-clean gag off his mouth.
"I interrogated him multiple times already, but he still kept his mouth shut." Song Zhihao informed, grumbling in annoyance at the man's stubbornness.
He even resorted in threatening to cut his fingers if he didn't start talking. But as you can probably tell, no body parts were cut off.
You can't blame him, really. His been out of commission from the Underworld for years. And his morals as a doctor was stopping him from returning back to his former self.
However, no one told him he couldn't just ask someone else to do the dirty work for him. By dirty work, he obviously meant torture and murder.