You are confusing the Cricket Trial and the Criminal Trial, and your facts are actually wrong.
These are the Facts:
1. All three players maintained their innocence to the ICC Tribunal - including Mohammad Amir.
2. Amir only pleaded Guilty in his criminal trial, but the honesty that involved was a joke anyway, as
a)
he continued to claim to have been born on 13 April 1992, to avoid being sent to an adult prison, and
b) he refused to give evidence of his crimes anyway at a Newton Hearing, leading the Judge to question the sincerity of his Guilty plea.
SOURCE:
http://www.thelawpages.com/court-cases/Mohammad-Amir-7586-1.law
3. The ICC Tribunal was clear that Mohammad Asif - not Amir - was the only one of the three to initially reject the corrupt approach, and that Asif - not Amir - was the only one to refuse to accept corrupt payments.