Will They Investigate Who Smuggled Drugs Into the Prison?

Possibly, but that is not the most pressing issue right now.

Your son is the one sitting inside with a dirty UA, a fresh set of charges, and fines stacking up. That is where the focus needs to be. Whatever happens to the person who brought the drugs in is largely out of his hands and out of yours, and spending energy on that question right now is a distraction from what actually matters.

Here is the reality. Facilities do investigate the supply side when drugs are found inside. If investigators believe someone on the outside was responsible for introduction of contraband, that person can face serious criminal charges. Smuggling drugs into a correctional facility is a felony in every state, and federal charges are possible depending on the circumstances. But whether they pursue that, and how aggressively, depends on what evidence exists, whether your son cooperates, and how much the facility wants to invest in the investigation.

That last part is the piece your son needs to think carefully about. If investigators approach him looking for information about who supplied the drugs, anything he says becomes part of a much larger picture that affects his own situation. He should not answer those questions without an attorney present. Full stop.

Right now, he needs legal representation focused on the new charges, the fines, and what this does to his existing sentence. The person who brought the drugs in has their own problems to deal with. Your son needs to focus entirely on his.