How does Nygma fake Stickley's suicide?

Question

In the 1995 movie Batman Forever, Edward Nygma (pre-Riddler) knocks out his supervisor Fred Stickley with a coffee pot, ties him to a wheeled chair, and uses him as a guinea pig for his prototype brain-manipulation device. When Stickley tells Nygma he is fired, Nygma pushes Stickley's chair towards the large window at the end of the lab. Stickley partially goes through the window, but because Nygma's device is strapped to his head and attached with a cable, he does not immediately fall. Nygma then removes the device and allows Stickley to fall several stories into the river below, effectively killing him. Nygma then stares directly into a surveillance camera before removing it.

The next day, Bruce Wayne is called into the same lab by Commissioner Gordon, who is investigating Stickley's disappearance. Nygma is shown being interviewed by police and hands them a suicide note from Stickley. Nygma (comically) informs the police that the handwriting, sentence structure, and spelling of the note matches Stickley's exactly, which strongly suggests that Nygma himself wrote the note.

Gordon, Wayne, and a handful of cops are then shown viewing surveillance camera footage of the previous night. The video depicts Stickley running through the lab, laughing maniacally, before jumping through the large window. The video does not show Nygma or anyone else in the lab at the time.

How did Nygma manipulate the security footage to show Stickley jumping through the window? CGI was in its infancy in 1995 so it seems unlikely that someone even as intelligent as Nygma could put together a video clip using such advanced animation, much less be able to mimic Wayne Enterprises' security video well enough to fool the police.

Answer 1

This was addressed in a piece of dialogue that appears in the film's official novelisation. The device E. Nygma was developing was capable of creating realistic holographic video as well as transmitting it. After creating the footage, Nygma (a video expert) merely had to splice it into the existing security tape

“Now you can be part of the show!” Nygma was proclaiming to the press and onlookers. “Nygmatech brings the joy of 3-D entertainment into your own home. Ladies and gentlemen. Let me tell you my vision. ‘The Box’ in every home in America. And one day the world. I’ve seen the future and it is me!”

Schoenfeld froze the screen on Nygma’s chortling expression, and he turned to Wayne. “We’ve been doing some preliminary market research of our own, sir. If this Box can really do what Nygma claims it can . . . cheap, easy to watch, 3-D holographic entertainment in the home . . . sir, we’re talking billions.

Billions that Nygma will be raking in for a device that he researched while in our employ.”

“You mean the device that Fred Stickley canceled research for.”

and

“And another name for Mystery?”

“Conundrum? Puzzle? Enig . . . ma,” he said, realizing.

“Exactly. Mr. E. Mister Edward Nygma. What wasted genius.” He gave a moment’s thought and then guessed, “The video of Stickley’s suicide must have been a computer-generated forgery. That must have been the night that Nygma first realized what his devices could do . . . and that poor bastard Stickley was in the wrong place at the wrong time.”

Answer 2

The most likely answer is Nygma's Remote Encephalogram Stimulator Box, the device which was initially being built to allow television to be projected into a person's mind directly, and was later modified to allow display of 3D images from the box. As implausible as it would be in real life, Nygma probably "reversed the direction" of the transfer, allowing him to substitute an imagined suicide (one which inplausibly has Stickley waving his arms about and laughing like a cartoon character before going out the window) and broadcast it onto the tape.