Saw IV (4) - Can somebody please explain what happened?

At the end of the movie when Hoffman (guy from the electric chair with Detective Matthews) was in the room where Jeff killed jigsaw from part III, and where the FBI agent gets locked in, you plainly see jigsaw dead on the table. Meaning this was the current moment of the movie. At the begining of the movie you see Hoffman get the tape out of Jigsaw stomach and that is his test. I think this is where he tells him he will help him carry out his work, meaning Hoffman's test. I don't understand how Hoffman got the cette out of jigsaw if at the end of the movie you see jigsaw dead on the table. how would Hoffman be helping if the tape is still inside jigsaws stomach. Remember at the begining its "live" and the rest is a flashback. When the FBI agent gets locked into the room Jigsaw is there and Hoffman was the one that locked them in? Maybe I'm not explaining my question right or maybe I missed something or don't understand. A answer will help Thanks in Advance.