The board chairman of the rail company blamed for a safety flaw in a deadly train accident has died of a heart attack while his company was being inspected by crash investigators, caing.com reported Tuesday.

Ma Cheng, chairman of a China Railway Signal & Communication (CRSC), collapsed at his office on August 22 as an inspection team arrived. He was taken to hospital where he was pronounced dead. He was 55.

The CRSC had become a target of public criticism in recent weeks after it was revealed an error in the company’s software caused the July crash killing 40 people.

The software, designed by the Beijing National Railway Research & Design Institute of Signal and Communication which is affiliated to CRSC, failed to switch a signal at Wenzhou South Railway Station to red after a train had stalled on the viaduct.

An unnamed source close to Ma said he shouldered too much pressure and responsibility and had no previous history of heart problems.