Answer!

Major General Bai finally received the verdict from the Disciplinary and Investigation Committee. The video evidence Ling Lan gave them was real. If this video was fake, they would commit suicide.

After obtaining Ling Lan's video, they compared it with the video sent by the unknown leaker. It allowed them to discover something amiss. Without Ling Lan's video, they wouldn't be able to notice the small problem with the first video evidence they had. This was why they took such a long time to reach a verdict.

Actually, the problem with the first video was Little Four's work. Little Four was someone who bore grudges. Hence, he messed with the video to take his revenge. He made a small change to the video. It was just a very small change but it made a very big impact. Anyone that wasn't stupid would be able to notice the change.