BEIJING -- An explanation by railway authorities for last Saturday's deadly high-speed train crash has raised even more public doubts about what had actually happened to the accident and to the government investigation itself.

A high-speed train rammed into a stalled train near the city of Wenzhou in east China's Zhejiang Province on Saturday, leaving 40 people dead and 191 injured. The accident was caused by "serious design flaws" in railway signaling equipment, an official from the Shanghai Railway Bureau said Thursday morning.

A lightning strike triggered the malfunction, which resulted in a green alert light failing to turn red, leaving railway personnel unaware of the stalled train, the official said.

The Beijing National Railway Research and Design Institute of Signal and Communication Co. (CRSCD), which was responsible for designing and building the signaling system, has posted an apology letter on its website, offering condolences and promising to "shoulder any due punishments that may result from the investigation."

However, the bare-bones explanation has done little to assuage the public's concerns.

The Beijing Youth Daily newspaper posed several as-yet unanswered questions in a Friday report on the accident. "Why was such seriously flawed equipment in use for nearly two years without being detected? Why was it installed in as many as 76 rail stations across the country? Are there other problems with the railway apart from equipment flaws?" the report asked.

The CRSCD held a press conference Thursday afternoon, during which it failed to answer many of the questions posed by journalists. Tian Zhenhui, a company official, avoided taking direct responsibility for the accident at the conference. Pressed by reporters, she said the company apologized only because it helped to build the railway.

She refused to specify which pieces of equipment failed, what other lines the equipment is installed on and how the equipment managed to pass tests and quality checks before being installed.

"Why haven't you suspended the operation of railways that have installed similar equipment? What if more accidents occur while the investigation is under way?" asked one reporter.

"It's a technical issue. I have no idea about that," Tian repeatedly replied, stressing that an official conclusion for the probe has yet to come.

"Premier Wen Jiabao has demanded that the probe into the accident be open, transparent and subject to public oversight, but the first person to apologize for the accident cannot even explain what responsibilities she has," the China Youth Daily said in its Friday report.

The Internet has become a significant outlet for public anxiety since the accident, with netizens taking to microblogs and message boards to voice their anger and concern.

"Mere signal failures cannot cause such accidents on modern high-speed railways. There must be more inside stories," an Internet user with the username "wangzhanghao8888" stated in the comment section of an article ran by sina.com, a major Chinese Internet portal, on the CRSCD's press conference.

Zhang Quanling, a news anchor with China Central Television, took railway authorities to task with a post on weibo.com, a popular Chinese microblogging site. Her post had been forwarded more than 24,500 times as of 2:30 p.m. Friday.

"Where else is the flawed equipment being used? Were the flaws checked and rectified by a third party before the railway resumed operation? If so, why was the problem not made public until today? If not, why were operations resumed?" she wrote.

Peng Kaizhou, China's deputy minister of railways, said during a Thursday investigatory meeting that the same flawed equipment is currently being used at another 76 train stations across the country.

The ministry started monitoring the stations early Sunday morning and will halt operations if it detects any malfunctions, said Peng.

The CRSCD is a subsidiary of the state-owned China Railway Signal and Communication Corp. (CRSC), which was part of the MOR until 2000, during which time the CRSC enjoyed a near monopoly in the railway signaling system market. It has provided equipment and technology for most of China's high-speed railways amid a construction boom in recent years.

In a closed market, products were introduced without adequate market competition and evaluation, said Meng Yanbei, a professor at Renmin University.

To the surprise of many who visited the website of the CRSCD, its allegedly flawed signal system was awarded "the Science and Technology Prize" by the China Railway Society under the Ministry of Railways in 2007, and its anti-lightning technology that failed to function this time won a third prize for engineering design of the ministry in 2009.