Almost Too Easy

Arvell concealed his presence and dashed at the boy situated to the far right of their group.

If there was evidence that the boys were killed, a thorough investigation would have been run to identify the culprit, but simply beating them up wouldn't garner that much attention.

Since Arvell didn't want any charges of murder, he wasn't able to upright kill them, but due to the examination rules, he wasn't really allowed to beat them up either.

If they caught him doing so, they would have failed him instantly.

While Arvell didn't fantasize about himself as some champion of justice, blatantly ignoring stuff like this while being able to stop it wasn't something Arvell was too fond of.

Hence why he decided to take a page from Lucas's little group.

If he wasn't caught, how would he get in trouble?

All he needed to do was make sure that no one there could identify him.

If he could break their line of sight, he wouldn't need to worry about being identified and punished.