2:24 PM PT -- Sources with direct knowledge tell TMZ ... early toxicology results from this investigation suggest traces of cocaine and fentanyl were found in the deceased's systems. A full toxicology report has yet to be released -- but for now, we're told these are substances that cops have detected early on, and there may be others that surface when the official results come out.

The mysterious deaths of 3 Chiefs fans might soon be cleared up -- and early signs point to it being drug-related ... so says an attorney repping one of the families of the deceased.

We talked to Tony Kagay -- a lawyer who's been hired by the mother of Clayton McGeeney, who was one of the three who were found dead in Jordan Willis' backyard -- who joined us on "TMZ Live" Thursday to tell us what he knows about the investigation thus far.

Kagay was certainly trying to keep his cards close to the vest here -- but based on a meeting he says his client, Nancy Bossert (Clayton's mom), had with authorities Wednesday ... it sounds like what people have suspected will soon be confirmed.

Namely, he seems to be suggesting that the autopsies are complete and early toxicology tests have been run ... and while he doesn't reveal the exact results, he does say he's privy to the fact that there may (or may not) be substances that were discovered in their bodies.

We pushed Kagay to tell us what he knew -- but he was being careful with what he said, and how he said it ... but you can read between the lines here and figure out what's what.

Basically, Kagay acknowledges that drugs may have played a part in the 3 men's deaths -- but there are still questions that need to be answered ... including how any substances may have gotten into their system, and what exactly played out over the course of 2 days.

Cops so far have reiterated that there's no evidence of foul play, and that they're not investigating this as a homicide --- something Kagay confirmed with us as well.

Like we said, there's still a lot to uncover ... but Kagay tells us he believes the autopsy/toxicology results will be released soon (even as early as Thursday) -- which will hopefully shed some light on this tragedy. In the meantime, his client has asked for privacy.

Nancy did say this about her son ... "Clayton was a beloved son ... Clayton was a caring father. Clayton was a loving partner to his fiancée, April Mahoney. His death under any circumstances would have been painful to everyone his life had touched. Under these unusual and confusing circumstances, it is even more difficult for the family to deal with."

We reached out to Kansas City PD and they told us they weren't aware of toxicology results coming anytime soon -- and simply said the case remains under investigation.