Shylock S 10 1, Shylock sent a message to Watson saying "If my brother has a green ladder, arrest him". What does that mean?

The Green Ladder is a solved case.

Go and see Sherlock's Deductive Science. There is a case about this green ladder. It is mainly about a woman whose husband drowned and asked Shylock to help investigate the cause of her husband's death. The woman thinks that her husband's brother killed him, but his brother has an alibi. Shylock found a green ladder on the road beside her husband's drowning pond, and found that the husband was a superstitious person. When superstitious people see a ladder, they feel unlucky to walk under it and want to go around it. Shylock also found that her husband had seen wine in the house before he died. He didn't drink enough, so he got drunk. When he walked to the pond in the garden, he saw the green ladder and walked around. As a result, he fell into the pond and drowned. The text message in Peanut's mobile phone was sent by Shylock to the woman whose husband died, telling her that if the ladder belonged to her brother, he was the murderer. In fact, it is also related to the plot. Watson saw this short message, and then went online to find the website of deductive science to see Sherlock's reasoning.