Retired Sligo Garda John Nicholson has been accused of setting up Bernard Conlon to make "false and malicious" claims in relation to the McBrearty family.
Former Donegal Garda Supt Kevin Lennon told the tribunal that Mr Nicholson was a "most deceitful person" who had misled him and had put the State in a "position of compromise" through his deceptions.
The tribunal has heard evidence that Mr Nicholson and other gardaí had told Mr Conlon to be caught in the McBreartys' nightclub in Raphoe drinking after hours so that he could be a witness against them in a licensing prosecution.
Mr Nicholson denies the allegation.
Mr Nicholson has been prosecuted for submitting forged employment certificates for Mr Conlon in order to secure expenses for him for court appearances.
In response to questioning from Tom Murphy, solicitor for Mr Nicholson, Mr Lennon said he had trusted Garda Nicholson and knew nothing of the set-up until it came before the tribunal.
"Your client set up Bernard Conlon to go to Mr McBrearty's pub, and make false and malicious claims on his behalf, and forge certificates."
Mr Nicholson had told Mr Lennon that he feared he might be arrested, before his prosecution for the forgery offences, but he had not told him why, he said.
"Why did he not come to me and tell me the truth that he forged those certificates? He caused the State to be put in a position of compromise and misled me in every way."
Counsel for Mr Conlon, Desmond Dockery, said there was a "golden thread" running through Mr Lennon's evidence that he "didn't know, were not told, and had no idea about things everybody else knew everything about."
