Watson has already served 18 months in an Australian prison after pleading guilty to negligent manslaughter, essentially admitting that he failed to save her.
Prosecutors in Alabama have charged Watson with murder, claiming Tina Watson's death was planned in the U.S.
Prosecutors claim Watson expected to collect $130,000 insurance after she died, but Watson's lawyers argue that he did not collect a penny following his wife's death.
Testimony earlier in the week drew tears from Watson as he listened to his own videotaped description of how his wife died.
A photo of his wife lying motionless on the sea floor was introduced as evidence and an Australian police officer testified that Watson was calm and cooperative until he was told he could not have his dive computer back.
The dive computer is a watch-like device that tracks a swimmer's dive. Watson and his wife quickly returned to the boat at the beginning of his dive because his computer was beeping. Prosecutors contend that was a ploy to get his wife away from other divers to kill her and that a computer wouldn't beep if the battery was in upside down.
Watson's legal team said in their opening statement that they checked with the computer's manufacturer and were told it was designed to beep if the battery was improperly installed.