HONG KONG — When a senior police officer’s investigation produced more than 150 arrest warrants this year, it was seen as a tentative success in Thailand’s pledge to crack down on human trafficking.

But last month, that officer, Maj. Gen. Paween Pongsirin, resigned, and on Thursday said he had fled to Australia out of fear for his safety, raising questions about the extent of collusion between crime syndicates and the authorities in Thailand.

“I’m not afraid of the good officials,” he said by telephone from Australia. “But there are bad police and bad military officers, and I know they are trying to get me.”

Mr. Paween had led an investigation into a mass grave containing at least 36 bodies that was discovered in May near the border with Malaysia. That inquiry resulted in charges against more than 90 people from Bangladesh, Myanmar and Thailand, including a lieutenant general in the Thai Army, Manas Kongpan, who is accused of being a trafficking kingpin.