One big mistake at the end

Rating: 2/10 (12 December 2019)

It was going towards an 8, but... only if there was a reasonable( or some at all) explanation of how did the black guy find them in the end?!? It took a genius, a mathematician, and the creator of the cube to get to the bridge. And suddenly, the guy who almost died a couple of minutes ago is there with them, came out without making any noise, and killed the woman. That screwed the whole movie for me! Not only it was unbelievable, but was impossible too. Why did they even do it? To get some more action from the movie.