IANAL, and this depends on jurisdiction, but it generally requires planning plus an overt act towards the plan. If I plan to kill my boss, saw him into pieces

IANAL, and this depends on jurisdiction, but it generally requires planning plus an overt act towards the plan. If I plan to kill my boss, saw him into pieces with a chainsaw, and put the pieces in triple-mylar garbage bags, when I go to the store to buy garbage bags I've crossed the legal threshold. In many states, if the prosecutor can prove to the jury 1) I planned to kill my boss, saw him into pieces with a chainsaw, and put the pieces into garbage bags, and 2) bought garbage bags, I'm toast and will go away for several years. NB there is nothing wrong with just buying the garbage bags.