Its true to say that when looking at it through the eyes of a person capable of experiencing remorse you would expect to see a bit more of an 'edge' but than what we've seen so far.
But delving further into the research it seems those who are capable of serial killing are usually also very skilled at impression management.
According to the article below those involved in inflicting crimes in a heath care setting may experience 'killing' differently. This, they put down to a few things. Firstly it's the desensitisation to death and experience of being among it, secondly it's the ability to adapt quickly in a death type situation. So to use thinking skills 'in the moment'
Article also refers to 'doubling' which allows perpetrators to develop two 'selves'
All very weird and bizarre but here's the article incase you are interested.
Healthcare serial killing involves the intentional killing of multiple patients by a healthcare professional. It is a formidable challenge to identify in the medical context, and a daunting legal task to prove beyond reasonable doubt. What can be done or remains to be done to intercept these...
link.springer.com