So far the possible culprits are:
SF
Reason: Acting Nervous, Quick denial. Named an unknown classmate named CASPER, when no one else has mentioned prior
CHARA
Reason: Accesses to medical devices, possibly used on Sketchy, Chaotic behavior.
*SKETCHY
Reason: Overall actions. Acts evasive when confronted. Possible Admission (?)
*SKETCHY is the most likely culprit with it being likely he received help from CHARA or SF