Liam Payne Eyewitness to Fatal Balcony Fall Haunted by Ghastly Images

Liam Payne's fatal fall was witnessed by a hotel guest who was at the CasaSur Palermo in Buenos Aires for his wedding, and he is haunted by what he saw.

Bret Watson was in a room on the first floor of the hotel with his wedding planner, and as they looked out the window they saw Liam in free fall. Bret appears in our new documentary, "TMZ Presents: Liam Payne: Who's to Blame?" airing on FOX tonight at 8 PM ET and streaming on Hulu beginning Tuesday.

Bret and the wedding planner ran to the balcony and looked down ... and immediately identified Liam, who he believes died instantly.

Bret says the sound of Liam's body hitting the ground was even more haunting than the fall itself, and it's apparent from the interview he's still having pretty severe emotional difficulty.

Bret and the wedding guests saw Liam throughout the day and noticed he was becoming more and more intoxicated and erratic as the hours passed. Bret saw the last encounter hotel staff had with Liam, as they carried him by the arms and legs from the lobby to his room, where they left him alone. A short time later, Liam fell from the balcony.

Bret's account is vastly different from Liam's good friend Roger Nores, whom prosecutors want to charge with abandonment. Nores insists when he left Liam the final time an hour before the fall, the singer was in good spirits and only a little tipsy.

According to official documents obtained by TMZ, the timeline shows Liam was on the hunt for cocaine early in the day ... even texting Nores he needed 6 grams.

Braian Paiz, a waiter whom prosecutors want to charge with supplying drugs to Liam, tells us he visited Liam twice during his stay, each time drinking whisky and doing cocaine, which Paiz supplied. He insists Liam did not pay him for the drugs.