(1) In a prosecution for an attempt, it is no defense that it was impossible to commit the crime which was the object of the attempt where the conduct engaged in by the actor would be a crime if the circumstances were as the actor believed them to be.

Clarification

a suspect can't defend against an attempt charge by saying it would have been impossible to carry out the crime at the time of the attempt if the circumstances as the suspect believed at the time of the attempt would have resulted in a crime. Example:

in order to collect on a life insurance policy, a subject leaves on an unlit gas stove in an attempt to asphyxiate the occupants of the house. However, unknown to the subject the gas had been shutoff by the gas company at the time of the attempt making it impossible to kill the occupants that way.

Even though it was impossible to murder the occupants as the gas was shut off, the subject would not be able claim a defence of impossibility because at the time of the attempt they believed that the gas was in fact switched on.