Is the act or the person committing the act evil? Or is it both?
Open any dictionary and you will find that almost every word has more than one meaning. This applies to your question.
Leaving the dictionary aside, but keeping the idea that a word can have two related meanings (at the minimum), let's look at a couple of differences between an act and a person.
An act is singular and occurs at a single point of time or a single duration.
A person commits many acts over life and has a much longer time frame than a single act.
This means that we can judge an act as a whole as good or evil, depending on the standard we use. (Moreover, not all acts are all good or all evil, but some are.)
When we call a person good or evil, the meaning of evil (or good) is not so all-encompassing. We generally mean that an evil person chooses to perform some, or many, acts whose vileness outweighs the good of his or her other acts. Also, by this meaning of evil, we implicitly refer to the time period when he or she is making such choices. We rarely mean the evil person was evil as an infant, for example.
Notice, also, that this evil can be reversed. In other words, if an evil person has a change of heart, feels remorse, repents, tries to make amends for the results of his or her evil acts, and starts doing good things, we no longer call that person evil.
However, an evil act is evil by its nature and there is no way for it to redeem itself. It has happened and its results have been set in motion. There's no way to make it un-happen or re-happen in a different manner.
In O-Land, you sometimes find finger-pointers who call people evil and they mean the term in the same way they use it for an act. They do not have a second meaning for evil. In other words, an evil person to them deserves condemnation only and there is no place for moral redemption. Once you are evil to them, there's no way to undo it. You always will be evil.
Sometimes these folks give lip service to the possibility of redemption since they believe it is rational to leave it on the table. But in practice, I have yet to see them absolve a person they once called evil. In fact, read O-Land discussions of forgiveness. You will find some people arguing that forgiveness is a sin in practically all contexts and cases because it is a form of negating justice.
These people have no heart, or at best, have a feeble heartbeat due to their hardening of the categories.