Broken security cameras along the getaway route used by the main suspect in last week's Bangkok bombing are complicating the investigation of the terrorist attack that killed 20 and injured 120.

National police chief Somyot Poompanmoung noted that two-thirds of the cameras were not functioning properly and openly displayed his frustration over the complexities of the circumstances, under which his forces were trying to "put pieces of the puzzle together," the Associated Press reported.

"For example, the perpetrator was driving away -- escaping -- and there are cameras following him. Sometimes there were 20 cameras on the street but only five worked. Fifteen were broken, for whatever reason, they didn't work," Somyot said. "The footage jumps around from one camera to another, and for the missing parts police have had to use their imagination. We've had to waste time connecting the dots."

Somyot alluded to the CBS crime series "CSI: Crime Scene Investigation," which follows Las Vegas criminalists as they use physical evidence to solve murders. Thai authorities lack sophisticated video equipment to render blurry images clear, he explained. "Have you seen CSI?" Somyot quipped. "We don't have those things."

As authorities continue their hunt for the main suspect, an unidentified man in a yellow T-shirt who apparently placed a rucksack under a bench at the Erawan shrine minutes before the Aug. 17 blast, around 100 mourners observed a minute's silence exactly one week after the incident, Agence France-Presse noted.

"I feel sad; the sadness has stayed with me," Nopparat Jantawisut told the French newswire. "The people who died here came with good hearts to make merit, but the result was the opposite." the 68-year-old added.

Meanwhile, monks dressed in saffron robes on Monday led prayers at the small streetside shrine that was the scene of Thailand's worst single mass-casualty attack.

The chief of the military junta in control of Thailand's government, Prayut Chan-O-Cha, meanwhile, ruled out that the country would ask foreign investigators to lead the inquiry into the bombing, though he said he was open to technical advice from overseas, AFP said.