Technically, it is classified as attempted murder. I think it would never stick as there is no proof so a prosecutor would not touch it. Anna knows this as well. Dex would need an email, text, or recording of Sonny giving the order. Dex stole fentanyl and a syringe. Went into a patient's room and intended to kill him.
Murder and Attempted Murder
Attempted murder is the failed or aborted attempt to murder another person. Just like other crimes, attempted murder consists of both an action and an intention. In attempted murder, a person must take a direct step towards the killing and must have the specific intent to kill that person.
The Action
In order to be convicted of attempted murder, a prosecutor must show that the accused took a "direct step" towards killing the targeted victim. Courts have explained the requirement for a direct step by stating that a person must go beyond merely preparing to commit the crime, and instead cross over into actually perpetrating it. Preparation is thinking about committing the crime, talking about it, or otherwise planning to do it, while perpetration is taking an action that puts the plan in motion and that would result in the intended killing. The kinds of actions that are enough to be a direct step differs from case to case, though there are a range of actions that can qualify, such as:
Stalking, tracking, or ambushing. This includes hiding out in waiting, tracking the victim down, or following the victim, hoping for an opportunity to commit the murder.
Luring. Includes trying to convince the victim to come to a specific place or take specific actions that will make it possible for the victim to be murdered.
Breaking-in. For example, unlawfully sneaking into a home, property, or other place where the victim is or thought to be.
Constructing. This might include collecting all the materials necessary for the murder, such as the parts of a bomb, and starting to put them together.
Soliciting. For instance, paying or convincing someone else to commit the murder, or even convincing an unknowing person to carry out a key part of the crime, such as unknowingly planting a bomb.