We can determine the veracity of Amrullah Saleh's preposterous claims from his past.

1. After Saleh became the head of NDS in 2003, he would regularly present a dossier of evidence to Richard Blee and others at the CIA. The evidence would assert something like... https://twitter.com/AmrullahSaleh2/status/1386201531322667010

“Colonel Mohammed is the Quetta Shura’s contact at ISI.” The CIA would run it by their ISI counterparts, who would reply, “We have a thousand Colonel Mohammeds.” Steve Coll writes that it was an objective fact that the Pakistani service had arrested and handed over hundreds...

...of foreign Al Qaeda militants —many more than NDS could even imagine. Gradually the CIA didn't take him seriously.

2. On January 18 2010, DG ISI General Shuja visited Kabul on the invitation of President Karzai who intentionally did not mention the visit to Saleh until...

...Pasha was already at the Arg palace. Saleh greeted the ISI chief. Karzai then asked him to leave the room. The implication was unsubtle: I don’t trust my spy chief.

As the conversation went on, Saleh waited in a reception area. While explosions echoed in the distance.

After the meeting, Karzai asked Saleh to escort Pasha to the airport safely.

“Do you have any leads as to who is doing this?” Pasha asked him.

“Yes, if you want, I can share with you—the attack is not finished, Mr. Director. The people inside the bank are communicating with...

..a number in Pakistan. They are taking instructions. Right now, while you are with me.”

“Brother, give it to me,” Pasha said.
Saleh wrote down the number.

“I will get back to you,” Pasha promised.

A week later, Pak military followed up on the number and arrested 7 Afghans.

The Afghans were over to NDS without publicity. But Amrullah Saleh went public with a statement that he had proof the whole thing had been an ISI operation. Pakistan concluded that Saleh was only interested in anti-Pakistan propaganda than cooperation.

3. After the US invasion of Afghanistan, the first CIA team landed with $10 million cash under Gary Schroen on Oct 7 2001. They established a joint intelligence cell with Saleh. As Schroen's lackey, he assisted while US dropped 12000 bombs; killing 10000 Afghans in that autumn

4. Infact, Steve Coll writes in his book that while Kabul was burning with charred bodies, @AmrullahSaleh2 was still dissatisfied with the atrocities and was further provoking the Americans:

“This is all the US Air Force can do”?

5. At another meeting when Saleh was head of NDS, General Kayani had given him a shut up call for his farcical statements.

“I don’t need to be taught intelligence by someone the age of my son,” Kayani said in Saleh’s account.

6. Engineer Arif and Saleh of the Northern Alliance’s intelligence wing had reported to the CIA that hundreds of disguised Pakistani military officers had maneuvered and fought with Taliban before September 11. The intelligence officers deployed in Kabul never found any evidence.

7. As of now, Amrullah Saleh has formed a secret death squad called ’Zarghoon Baheer’. He has killed many innocent Afghans from journalists to politicians. The intent behind maligning Pakistan with ludicrous stories is to hide the extra judicial killings he has been carrying out.

Reference:

1. “Directorate S: The C.I.A. and America's Secret Wars in Afghanistan and Pakistan” by Steve Coll
2. “The Way of the Knife: The CIA, a Secret Army, and a War at the Ends of the Earth” by Mark Mazzetti