On-going Cases

Rated ⭐⚝⚝

What animal is this?

Clue: Pay attention to where the stain is

Case 2

Credit to a French Detective.

2, November, 2023

Rated ⭐⭐⚝

It was the case of the bank cashier from Chigwell, a man in his fifties, found murdered in his home. He and his wife lived there alone, forming a happy and uneventful couple.
His wife was preparing dinner when she heard the sound of a conversation in her husband’s office. Intrigued, she approached, but the door was locked. She heard her husband scream, and then there was silence. She left the house and went around to the window of the office. This window was open, which was rather curious for that season.
She drew the curtain and saw her husband lying dead with a dagger in his chest. No one had come to the house, and it would have been difficult for anyone to enter and exit discreetly because the office window faced the front of the house, visible to the neighbors and everyone.
The police focused on verifying the woman’s statements. The intruder had left no trace of their presence, and what had driven them to murder an innocent bank employee left them completely puzzled. Their investigations led them to consider the possibility that the banker may have been privy to sensitive information, compelling enough to warrant his murder. His wife was quickly cleared of suspicion due to her arthritic hands, significant enough to prevent her from stabbing her husband in the heart. He had no enemies or rivals, no lover, potential criminals, or colleagues who could benefit from his absence, and none of his relatives had suddenly become wealthy – his will was written in favor of his wife, who inherited his property.
Holmes seemed to find the case insultingly simple, which vexed me when I had to wrack my brain to find the answer.

What do you think happened?

The answer needs to explain all the detail in the scene. The wife, clean scene, open window, curtain was out, the conversation, sensitive information, etc.