Metropolitan police chief Pol Lt-General Sanit Mahathavorn on Sunday gave an update on the investigation into the accident in which a large metal support structure fell from concrete pillars, killing the men.

He said police had finished interviewing 12 witnesses and were ready to issue the arrest warrant.

“Police will issue arrest warrants for one or two persons responsible for the accident, including the engineer whom, it was found, was not around to supervise the construction work at the time of accident,” Sanit said.

The crane driver at the site told police that the crane was stiff, so he pulled it backwards, but the joints could not resist the pulling force, causing the crane to fall and cause the collapse.

Police said they investigate where or not the crane driver was properly licensed and experts would examine the crash scene to assist in the probe.

Since the construction on the Red Line Skytrain started in February 2013, there have been six accidents and eight worker deaths.