Hong Kong's embattled government is to investigate whether Tuesday's derailment on the East Rail line was sabotage, the Post has learned.
As the mystery over the cause of the accident deepened, one line of inquiry turned to whether disgruntled MTR Corporation employees were behind the incident.
"Many possibilities have already been ruled out after further checks, so the Hong Kong government will look into whether the derailment was an inside job," a source said.
"So far, the MTR Corporation still has no clues about the probable cause of the incident."
The Electrical and Mechanical Services Department (EMSD) said it would examine various factors, including the mechanical parts of the train, the track and associated devices, as well as the possibility of obstruction by foreign objects.
It also emerged on Wednesday that a fourth crack had been found on tracks at the scene of the city's most serious rail accident in more than two decades.
Five passengers were sent to hospital, and 500 others were left in shock, after the 12-carriage train derailed as it entered Hung Hom station at around 8.30am. Three carriages veered off the tracks at a junction where trains are directed to different locations.
Services on the East Rail line, the city's only local line connecting it to the border with mainland China, were disrupted for most of the day.
On Wednesday, the MTR Corp's chairman Rex Auyeung Pak-kuen met union leaders for the first time to address concerns over division within the company.
Tam Kin-chiu, vice-chairman of the Hong Kong Federation of Railway Trade Unions, said: "At the meeting we raised the point that some people suspected to be MTR staff might have leaked the company's internal information on social media.
"The chairman said it was hard to investigate such allegations, but he hoped that the MTR staff would not do something to harm the company. He also expressed hopes the staff would treat each other as a big family."
Tuesday's accident dealt another blow to the beleaguered rail operator, which has been targeted in recent weeks by anti-government protesters who have vandalised more than half of its 91 stations.
The wave of anger at the MTR Corp followed multiple incidents of clashes between protesters and police in stations and trains, as well as a mob attack in Yuen Long.
The corporation had also been accused of bowing to pressure from Beijing by closing stations before demonstrations began.
The cause of the derailment was not yet known, although the rail firm and the government, which is a major shareholder, have vowed to conduct a thorough investigation.
Transport minister Frank Chan also said nothing was being ruled out, but police have said they found no suspicious objects at the scene.
Cheung Kim-ching, chief engineer of railways at the EMSD, said on Wednesday that part of the track was completely torn apart by the fourth crack, where there were two fractures measuring 30mm and 45mm in width.
It followed the discovery of three cracks on the track on Tuesday, two of which were each about 30mm wide.
"It will be one line of inquiry. We will invite experts to examine the material on whether the cracks were the cause or the result of the incident," Cheung told a radio programme.
In a statement released on Wednesday night, the EMSD confirmed it had not found any foreign objects on the section of track.
"The department is deeply concerned about the serious incident … It will conduct an independent, thorough and in-depth investigation, and seek advice from overseas experts," it said.
Former railway chief and lawmaker Michael Tien Puk-sun said originally he suggested a malfunctioned railway switch lock at the diverting point could have caused the incident.
"I raised this with the MTR, but after checking, they confirmed the lock functioned properly so this possibility was ruled out," he said.
Tien warned that if the MTR could not identify the cause quickly, it would trigger more public fear over the safety of the city's railways.
Some trains on the line from the Lo Wu and Lok Ma Chau border districts terminated at Hung Hom on Wednesday, but the service ended at Mong Kok East station for others. Trains from Hung Hom to Mong Kok East station were running at regular seven-minute intervals.
Services left Mong Kok East for Lo Wu station every 31/2 minutes, while passengers going to Lok Ma Chau had to change at Tai Po Market station, where trains were running at 12-minute intervals.
The wreckage of the derailed carriages had been cleared by morning, while one track remained closed and blocked off with orange netting. The derailed train was stationed at the closed Hung Hom-Lo Wu platform.
The rail operator was expected to be fined HK$25 million (US$3.2 million), the maximum financial penalty available, for Tuesday's service delays, according to lawmaker Ben Chan Han-pan, who heads the legislature's transport panel.
About 200 staff worked overnight to remove carriages and carry out safety checks and repair work.
Danny Chiu, an engineer who lives in Wong Tai Sin and commutes to Hung Hom from Mong Kok East, said he was worried about future incidents, while also commending the rail operator for working through the night to restore service.
"I was not affected yesterday as I just took a different route to work. But I do hope the MTR can run smoothly with no other incidents from now on," Chiu said.
Quentin Cheng Hin-kei, a spokesman for commuter concern group Public Transport Research Team, said the incident had raised mounting concerns over the adequacy of the MTR's maintenance system, and the government's monitoring of the rail operations.
"The incident has shown there are loopholes in the MTR's maintenance system, and the government has been too passive in monitoring the rail operation. All it has done is to rely on the MTR for providing information," he said.
"The government should set up its expert team and set out a monitoring mechanism to ensure that the firm has fulfilled all the safety requirements," he said.
Copyright (c) 2019. South China Morning Post Publishers Ltd. All rights reserved.