Hanoi police have arrested Nguyen Xuan Khoat, Pham Anh Tam, Pham Duc Chung and Pham Van Duc for kidnapping a man and demanding VND500 million (US$23,900) in ransom.
The arrestees, aged between 22 and 26, will be investigated for the crimes of illegal detention and extorting property.
Police on June 11 received a report from Vu Thi Thu Trinh alleging people had called her saying they were holding her husband Le Xuan Binh hostage and would kill him if she did not pay the ransom, VietNamNet reported.
Trinh said they asked her to pay money to some loan sharks in Hanoi, repeatedly threatening to cut off Binh's fingers and take him to an isolated island for detention.
She said she reported the situation to police after failing to borrow enough money from her relatives and friends.
Hanoi police later found that the kidnappers were holding the victim at the Len Ly hotel in Quang Ninh Province's Ha Long Town.
Police busted into the room, arresting the kidnappers and rescuing Binh who had suffered minor cuts on his face.
Preliminary investigations determined that Binh had owed Vu Duc Tho of Hanoi's Dong Da District up to VND3 billion ($143,370) from betting on so de, an illegal numbers game based on the state lottery, allowing players to bet any amount they want for payoffs up to 80 times their original wager.
On June 10, Tho asked Khoat and his men to follow Binh and they captured the victim at a hotel in Hanoi.
The thugs drove Binh him around in a car as they beat him.
By midnight, they had taken him to the hotel in Quang Ninh, forcing him to call home and request the ransom money, as well as sign a VND5.6 billion writ of debt.
Police are investigating how Tho may have been involved; they did not say why he was not arrested.