Pakistan's triple train crash, in which 133 people were killed, has sparked off a major controversy among railway officials.
While some of them allege sabotage despite President Pervez Musharraf strongly ruling out such a possibility, some others blame it on 'defective' engines imported from China.
A third group of officials are of the view that the accident was the result of the driver of the Karachi Express overshooting the red signal and ramming into the stationary Quetta Express.
An inquiry has been ordered into the train crash at the Sarhad station near Ghotki.
The accident also brings into focus the new set of diesel engines being imported from China by Pakistan Railways with a senior minister questioning their quality.
Musharraf visited the accident site on Thursday and told reporters that all necessary action will be taken to identify the cause of the accident. He promised that the guilty will be punished.
On Wednesday, he had firmly ruled out sabotage and blamed it on negligence. An unnamed Pakistan railway official has questioned the conclusion that it was not sabotage.
"Looking at circumstances based on information received and keeping in mind standard operating procedures, it is almost impossible for a train to crash into another while ignoring all signals and for another train to be cleared to head for the same station in which a passenger train has broken down," local newspaper Daily Times quoted the official as saying in Lahore.