To be more accurate, the DSM refers to a, "lack of remorse", in order to make a distinction (albeit arguably a semantic distinction) with lack of empathy being reserved for psychopathy. To me, it's confusing because it implies someone can be empathetic while having no remorse. Practically speaking though, the DSM criteria implies a lack of empathy and remorse. It's impossible for clinicians to measure the exact amount of empathy or remorse someone has, so, "lack" can either mean the clinician estimates there is absolutely none or severely low.

It depends on the exact circumstance, however, deriving pleasure isn't a motivator because it's either extremely low or non-existent. The violent acts may be done for other reasons, such as wanting something when the person refuses to provide.