Another post here says "it took weeks 10+ hours day to fins it", which sounds like a major fuck up if that results with you are missing a deadline or cutting features
Is it? As the tech lead, it is his responsibility or fault either way that such errors do not make it the code or find them if that happens. If the project is delayed and you miss some big sale day or something, it does not sound so unfair that his bonus is cut.
I am not fully sold on the idea of him losing a bonus is 100% because he defended the person who did it.