The investigation into Thailand's worst ever bomb attack last week has been hampered by broken security cameras in central Bangkok, Thailand’s police chief said Monday. Authorities are looking for clues to the whereabouts of the suspect who is believed to have planted a bomb in a backpack at the Erawan Shrine.

Police are trying to "put pieces of the puzzle together" to find the bomber as several street-side security cameras were broken and unable to record the suspect's movements, national police chief Somyot Poompanmoung told the Associated Press (AP) Monday. Somyot had previously said that police would "need some luck" to track down the suspect amid reports he had already left the country.

"The footage jumps around from one camera to another, and for the missing parts police have to use their imagination," Somyot reportedly said, "Sometimes there are 20 cameras on the street but only five work,” he said, adding: "We have had to waste time to put the dots together."

Hundreds of guesthouses, apartments and popular tourist spots are being searched by Thai security officials in a bid to catch the suspect.

"There are more than 10,000 places in Bangkok that we have to inspect and search," Bangkok Metropolitan Police chief Lt. Gen. Srivara Ransibrahmanakul reportedly said. "We may also need to repeat searches at some places."

Srivara also reportedly said that authorities have questioned more than 10 witnesses and are planning to interview the survivors of the blast, which claimed 20 lives, including that of 14 foreigners.

Police released a sketch of the suspect and issued an arrest warrant against him Thursday after he was seen in a surveillance video placing a backpack in the shrine and then escaping the scene. On Friday, police raised the bounty for any information leading to the arrest of the suspect to 3 million baht ($85,000).

Meanwhile, on Monday, a construction worker found a grenade buried in a residential area miles from central Bangkok, police reportedly said, adding that they believe it is unrelated to last week's bombing. Lt. Sakon Rungkiatpaisarn of Pra Kanong Station told AP that workers at the site were unaware where the grenade came from, adding that a police explosives squad was sent to defuse it.

Nearly a week after the Bangkok bombing, authorities appear no closer to identifying suspects or a motive, while officials have issued contradictory statements about the suspect's appearance, the number of accomplices he might have had and the chances of foreign involvement, according to reports.