Speaking to Brianna Keilar on CNN's "New Day," Gocke said she saw Schwab falling down the Verrückt slide, leaving a trail of blood as he went. The raft that was holding him seconds before was in front of him.
"When I heard a noise that didn't sound like it was supposed to come from that kind of ride, that's when I turned around," Sanford said.
"I didn't understand what was going on so I only saw Caleb sliding down the last half of the slide, and then I saw the blood."
Sanford recalled that as Schwab hit the end of the slide, his friend, frantic, called for help, with medics trailing soon after.
"They realized that he was dead, so I don't think they tried to revive him," Sanford said. Medics then tended to two women who had been riding in the same raft as Schwab and who sustained minor facial injuries.
The Verrückt -- the world's tallest water slide, at Kansas City's Schlitterbahn water park -- is known for its unparalleled, 168-foot vertical drop.
Sanford and Gocke, both teenagers, had just ridden the slide earlier that same day.
Gocke described the raft's Velcro seat belts, and remembered testing out the straps to see how secure they were. She said she wriggled out of them without much effort.
"You'd think for something that's supposed to be known for being the tallest slide in the world they'd have a little bit more secure straps than Velcro," Sanford said.
Police said Schwab's death was due to a neck injury but are still investigating the circumstances of the deadly accident. The boy was the son of Kansas state Rep. Scott Schwab and his wife, Michele.
Schlitterbahn was to reopen at noon Wednesday, but the park said the Verrückt slide will remain closed for the rest of the season.