Fired From A Job; How To Explain It To Future Employers

Recently,  this mail hit my inbox.
“I hope you day is fantastic. I have been a keen follower of the articles you post on career point Kenya.
My career seems to have stalled following dismissal from my former employer. I would really like to discuss this with a specialist like you. I really need to get back on track.
I am a Finance professional with 5 plus years experience working in the Banking Sector. I have worked with 2 prominent Banks in Kenya; one for 3 yrs and the other for 2 and 1/2 years. My last position was an Operations Officer post.
I was terminated 10 months ago together with my boss who was the Operations Manager at the Bank for allegedly colluding with him in misappropriation some money for claims by customers.
To be clear on this, I realised that the bank was short of claims money for the customers like 2 months before termination. I told my boss on the same and from his response I suspected he was aware and could be part of the game. He just said we can deal with the customers later as it was promotion time and dealing with such a case then could mess up the promotion letters. Unfortunately, before the promotion period was over, we got letters from the Head Office to fire us both. My letter argued that I should have told the branch manager if my supervisor was reluctant to act.”
The reason I agreed with him was that he boss and I also wanted a promotion too. Anyway, I also feared to report it further as I did not want to expose him as a person who does not act on issues or undermine his work by portraying him as incompetent.
Since then, my life is filled with regrets , rejection, frustration and depression. I now work part- time with meager salary which does not meet my monthly expenses. Worse, I have a family that relies on me and am already having issues with my wife since I cannot provide and she is not in a very stable job. I also had a bank loan with the bank that I worked for and since my termination the rate of repayment (5%) was changed to the normal rate 18%, since am no longer an employee.
I have tried looking for jobs both online and from newspapers but am not able to land a job with any company. My CV is good and has opened the doors of interviews for me; having gone for 5 interviews. The interviews sessions are usually smooth, however, the question of why I left my last job screws me up. I honestly admit to being terminated and give the reasons for my termination. The potential employer then calls the Bank and later writes to me a regret letter explaining that “the report from my previous employer questions my integrity.”
I have since then changed my referee from the bank but I feel this has been a HUGE red flag; I am feeling somewhat black-balled. I wonder whether I should lie on the reason for being terminated or tell the truth? Should I also ask the HR manager to lie on my reason for termination and if so how do I make her do it?