Aaron Hernandez wrote "John 3:16" in blood on the walls of his cell -- and also in ink on his forehead -- before he hanged himself in his Massachusetts prison cell ... this according to the police report. 

TMZ Sports has obtained the official report which says officials at Souza-Baranowski Correctional Center found Hernandez in cell #57 around 3 AM on April 19. 

In addition to "John 3:16" written on the walls in blood -- officials say there were also several drawings in blood ... though the report does not specify what the drawings were of. 

Officials say under the drawings was a Bible opened to the passage "John 3:16" with the 16th verse marked in blood. 

"John 3:16" is essentially the centerpiece of Christianity -- "For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life."

The door had been jammed with cardboard -- apparently to prevent people from entering the cell to save him.

When officials broke through, the floor was covered in shampoo to make it slippery -- apparently to prevent Hernandez from gaining his footing in case he wanted to stop himself from hanging. 

He had also covered the window to his cell with a sheet which is what alerted officers in the first place. 

The report says Hernandez had a fresh cut on his right middle finger and there appeared to be large circular blood marks on each of his feet. 

The report also confirms the presence of 3 handwritten notes in the cell -- though the contents of the notes have been redacted.

Investigators -- including a handwriting expert -- analyzed the notes and determined they were written by Hernandez.

Officials say surveillance footage shows Hernandez talking on the phone "just prior to his cell door being locked" for the last time. Officials went back and listened to the call and determined there was no apparent indication of an intent to harm himself.