Police in Argentina are moving full steam ahead in the Liam Payne death investigation … raiding the hotel where the former One Direction singer plunged to his death.

Law enforcement sources tell TMZ … cops in Buenos Aires showed up at the CasaSur Palermo Hotel Wednesday night to review electronic and paper records following the October 16 tragedy in which Liam fell from the third-floor balcony of his room into a courtyard.

Our sources say Liam’s initial autopsy results revealed he had “pink cocaine” in his system, a dangerous cocktail of various drugs such as meth, ecstasy and ketamine, as well as other narcotics.

We’re told police examined information contained in folders and on laptops with hotel employees to determine who sold Liam the drugs. They seized documentation, film records and videos of the hotel’s underground area.

Our law enforcement sources tell us they are particularly focused on one hotel employee who may have sold drugs to Liam.

What’s more, investigators believe Liam fell to his death in a state of semi or total unconsciousness because of the position of his body when it was found, showing he did not try to protect himself.