Struggling is futile, the man thought grievously. The binds were too tight that it almost cut his blood circulation off. And under these people's watchful eyes, he doubts they'll allow him to have even a slight bit of chance to loosen it for his convenience.
But the doctor did remove 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 old, lawless 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.