The bomb that injured 14 people in a failed gold shop robbery in Hanoi last week was activated by a remote device, while another one which did not explode was designed to be set off by a mobile phone, police say.
A VnExpress newswire report Monday quoted Colonel Nguyen Van Quyen, chief of Hanoi police's criminal techniques division, as saying that Ta Van Thanh, 25, activated the bomb as he was fleeing the scene when his attempt to rob the Hoang Tin Gold Shop on Thursday failed.
His brother, 20-year-old Ta Van Hai, was his accomplice in the crime.
He left behind another bomb which was "more dangerous and more sophisticated," Quyen said.
The unexploded bomb, which weighed over two kilograms, was deactivated on the spot.
Thanh, who was arrested almost immediately after the explosion, told police that he made the bombs himself with instructions from his friends who worked as stone miners in the northern province of Lang Son.
However, the VnExpress report said miners in Vietnam were still activating bombs with long electrical wires as fuses and did not use remote controls as Thanh did.
The news website also quoted an unnamed police official as saying that several mining sites in the outskirts of Hanoi are using explosives, and that despite strict regulations on industrial explosives, people still trade in them easily.
For example, to break a big stone, it takes ten kilograms of explosives, but experienced miners can do it with just eight kilograms, so the remaining two kilograms will be sold to others, he said.
The official warned that control over chemicals in Hanoi is also lax so people with knowledge about chemistry can make mines and bombs easily.
Initial information from police is that at 11 a.m. Thursday Thanh dropped Ha off at an intersection near the shop to act as a lookout and then entered the shop armed with a handmade bomb in a plastic bag, a knife and a taser.
He handed the shop owner, Vu Hai Duong, a piece of paper which said he would activate the bomb if he was not given the money he asked for.
Duong asked Thanh how much money he needed, but grabbed the bag and threw it out of his shop, shouting for help.
Thanh fled immediately and was chased by some employees from a shop next door. The bomb exploded, destroying part of the shop and nearby vehicles, injuring the shop's employees and passers-by.
Thanh was arrested 20 minutes after the explosion, while Ha was arrested a day after. He had gone into hiding at his hometown in the northern province of Bac Giang.
Police are investigating the case further.