Tom Cassidy was a wealthy man with an 18-year-old daughter. He purchased the Harris Street Property as a wedding gift for his daughter. The purchase price was $40,000 and the realtor was Lowery Real Estate. Cassidy paid George Lowery the $40,000 in cash.
Cassidy was a bit of a drunk and a flirt. He flirted with Marion Crane at the real estate office, and hectored George Lowery into joining him for a night of heavy drinking to celebrate, although Mr. Lowery is concerned about such a hunk of cash in his office. After Crane stole the $40,000, a conversation is playing in her head about an enraged Cassidy demanding they get to the bottom of this, and Lowery retorting that he warned Cassidy to convert that kind of cash into a check like most clients do.
Cassidy then hired a private investigator named Milton Arbogast to track her down.
When Norman Bates murdered Marion, he cleaned her cabin of all her personal possessions including the embezzled cash (which was concealed in a newspaper), and put them into the trunk of her car, drowning it in a nearby swamp. The final scene of the original film shows police using heavy equipment to retrieve the car from the swamp. It could be assumed the car was searched and the ill-gotten money was returned to Tom Cassidy.