Who stole sydelle pulaski's shorthand notebook?

In the novel "The Westing Game" by Ellen Raskin, the character Sandy McSouthers, who is also Sam Westing in disguise, stole SyDELLe Pulaski's shorthand notebook. Sandy McSouthers is revealed to be the mastermind behind the elaborate game set up by Sam Westing to solve his own murder. SyDELLe's shorthand notebook contained valuable information that Sam Westing needed to carry out his plan.