"We try to find the conditions and negligence that led to the strengthening of position in a scandal that has badly on cricket in Pakistan," he said.
"When the scandal took place, we had an anti-corruption officials at the time with the team and want to know how this thing has happened."
Salman Butt, Mohammad Asif and Mohammad Amir received sentences ranging from six to 30 months on Thursday, their role in gambling-inspired plot in a bowl a deliberate no ball in the fourth Test against England last year of the Lord .
The three former internationals already been banned by the International Cricket Council (ICC) for at least five years when the news of the plot was first published in September last year.
Ashraf, who has transferred to the PCB chief last month, also said that sending a letter to the International Criminal Court reaffirms its support for Pakistan's anti-corruption unit of the world governing body.
"PCB will never support the players who are involved in corruption or fixing. We want to ensure that the ICC, we will cooperate with any investigation conducted by them," he added.
Media reports suggested the ICC anti-corruption and security unit could launch a more detailed investigation on the location of the claims on the basis of the evidence before the Southwark Crown Court in the trial of three players.
Ashraf said the PCB requests the Government to legislate an Act of Parliament which makes fixing and corruption in cricket a criminal offense.