When Silva left the arena, he quickly went through a portal back to the labyrinth and into Lisa's lab.
"Lisa, there is something I need you to take a look at." Lisa was busy working on something, but she turned her attention to Silva as soon as he walked in.
Silva handed her his sword, covered with the blood of the boy he killed. He was suspicious of the energy that was in that boy.
It wasn't to the extent that he would have cared to find out, but when he saw that the teachers didn't try to apprehend him for killing, he understood that they knew something.
They knew what energy that boy was exuding, and they knew it was a risk—and Silva had stilled the risk.
Now, Silva's curiosity was piqued, so he decided to find out what exactly it was.
The blood had begun to dry, so Lisa scraped some off into a small crystal plate and infused her mana into it, breaking it down to understand the composition of the blood.