Why is the father a suspect in the speckled band?

In Arthur Conan Doyle's "The Adventure of the Speckled Band," the father, Dr. Grimesby Roylott, is a suspect because he has a clear motive for wanting to eliminate his stepdaughters. He stands to lose a significant inheritance if they marry, as their late mother stipulated that they would receive money only if they were alive and unmarried. Additionally, his violent and erratic behavior, as well as his history of criminal activity, further implicate him in the mysterious circumstances surrounding the deaths of his stepdaughter Julia and the attempted murder of Helen.