The film stars Tobin Bell, Scott Patterson, Costas Mandylor, Betsy Russell, and Lyriq Bent.

However, it is revealed that John had planned for his death and left behind a series of recordings and clues that would lead investigators to his final game.

An autopsy of the Jigsaw Killer reveals a wax-coated microcassette in his stomach, and Detective Mark Hoffman is called in to listen to it.

She was once pregnant with a boy named Gideon but suffered a miscarriage when Cecil, a drug addict, robbed the clinic at which she was employed and accidentally slammed a door into her stomach.

Ignoring past clues that she is in danger, Perez leans toward Billy and is critically injured by shrapnel when its face explodes.

After Cecil got out when the trap broke, he lunged at Jigsaw to attack him but fell to his death in a mesh of razor wire.

Strahm makes connections from Jill's story to the Gideon Meat Factory, the scene of Rigg's final test.

Hoffman, who was never in any danger and is revealed to be Jigsaw's other apprentice, rises and seals a dying Rigg and a bewildered Strahm in the factory.

[3] That following month, Darren Lynn Bousman, who previously directed Saw II and Saw III, was announced to return as director.

The executive thought that the duo's script could serve as a prequel to the first film, detailing a traumatic event in Jigsaw/John's early life.

However, producers Mark Burg and Oren Koules did not want to do a prequel and dropped the idea, but the script led Dunstan and Melton to be hired to write the next three Saw films.

[8] Like in previous entries, rewrites took place during the writing process, leading many unused ideas for the film to later be recycled for Saw V.[9] Even though Tobin Bell's Jigsaw Killer character was killed off in the previous entry, in March 2007 it was announced that he signed on for Saw IV and Saw V.[10] With a production budget of $10 million production budget,[11] principal photography took place from April 16, 2007 to May 3, 2007 in Toronto.

[14] Lionsgate held its fourth annual "Give Til It Hurts" blood drive for the Red Cross.

"[21] Metacritic, which uses a weighted average, assigned the film a score of 36 out of 100, based on 16 critics, indicating "generally unfavorable" reviews.

"[24] Frank Scheck from The Hollywood Reporter said "the famously inventive torture sequences here seem depleted of imagination", but added that "it hasn't yet jumped the shark like such predecessors as the Nightmare on Elm Street and Friday the 13th movies eventually did.

"[26] James Berardinelli wrote that "Saw IV functions as a drawn-out, tedious epilogue to a series that began with an energetic bang three years ago with Saw, then progressively lost momentum, coherence, and intelligence with each successive annual installment.