More recently, however, traffickers have adopted new tactics to avoid detection. Zhang noted that they now use encrypted messaging apps and underground financial networks, and deliberately separate drug deliveries from money transactions.

"This makes tracking them and collecting evidence much more difficult," he said.

To young people considering a career in secret investigation, Zhang offers both encouragement and a word of caution.

"I hope more young people will join this field — to fight for justice and help protect society from the harms of drugs," he said. "But it's not for everyone. The job demands quick thinking, emotional control, and strong communication skills."

"It's like improvisation," he added. "There's no script. You walk in with a rough plan, and everything else depends on your intelligence and instincts."