Factual error: The whole episode is run as if based in the UK, and yet the script has obviously been written by an American. The UK does not have autopsies, it has post-mortems. The UK does not have a trunk (of a car) it has a boot.
A Very Good Year for Murder - S4-E17
Visible crew/equipment: After Tony is cured he exits toward his car. A big screen used for lighting is reflected on the side of the car.
Answer: In a flashback scene, it was shown that he had a violent temper, so it stands to reason that he finally killed her in a fit of rage.