I am working in a research team that consists of researchers and a team lead. The team lead asked me with another teammate to experiment with several methodologies to get good results on a data. When we presented the results, we found that my teammate was getting good results compared to my results. Thus, the team lead asked me to have a meeting with the teammate to understand why my results are not good.
During the meeting with my teammate, I found that he has an issue with the way he is producing his results; he was working in a way that is biased and incorrect (he wants to get good results in anyway, and I don't know if it was intentional). I mentioned the issue to him and he understood it.
Later on, we had a meeting with the team lead again to discuss the results. He asked my teammate why there were differences in the results, and my teammate answered with a different reason. So he answered with something else to hide that he had an issue.
I didn't say anything because I felt that this will make our meeting weird and make him looks like a liar (which is actually the case). My team lead asked us to work more on the results to align them following the "wrong" reason that my teammate responded with.
I didn't like what happened and I was thinking to report that to my team lead, but I didn't want him to think that I am snitching. Also, I don't want him to talk to my teammate and then our working environment will be "weird".
What do you suggest me to do?
p.s. I noticed something in my teammate's behavior that he always acts as if he is sure of everything (in public meetings), but when I have private meetings with him, I find many issues in his work. Because of that, I thought that what he was doing is intentional to make him look good.