Well, I'm 6 years late to the conversation; but there is a scene where Ms. Ashcroft, Wayne's financial manager, explains to Columbo that Wayne, while not the beneficiary of Theresa's will, is the beneficiary of Theresa's life insurance policy. In fact, Ms. Ashcroft drew up that policy at Theresa's request, and it had a hefty face value.

Wayne had earlier taken out a life insurance policy on himself in which he made Theresa the beneficiary. When Theresa discovered this, she wanted to reciprocate and do the same for Wayne.