I think MM was done with life in general and he wanted to make MT 'done' too. Couldn't stand to see her doing well and so happy. His attempts at covering up were childish and a vascular surgeon would surely be smarter than that if he truly cared and wanted to get away with it.
JMO
I think this is one possibility, he was done with life and did not care anymore.
However I could argue that he did think he would get away with the crime. We have to understand that his typical mode was functioning like a child. He was trying to evade the attorneys from his lawsuits, acting like a child with address changes and refusing to accept subpoenas. And not moving on from a marriage long over. Sending threats.
He was struggling to pass his credentialing exams. Failing to function on the job. An adult buckles down, gets help, tutoring, mentoring. Whatever it takes to succeed in their goals. A child has a temper tantrum and starts throwing toys out of his crib,
This is mental illness and part of the picture is his functioning on a the level of a child.
It is possible he thought would get away with the crime. Narcissists often think they are the smartest people around. Everyone else is stupid. Even though in many areas of life they are totally incompetent.
He did make an attempt to cover up the crime with the phone and license plate tricks. And he did visit the home beforehand to reconnoiter the future crime scene. Mostly he wanted to figure out entrance and exit, damage the alarm system, break a basement window, etc. Also most likely he left something in the home, stalkers usually do. Surveillance equipment, something personal so that MT would know he had been there, etc.
He thought he could provide an alibi to the police, and that he could talk his way out of the crime, they would have no proof. He thought he could successfully commit this crime and get away with it.
Like most narcissists they vastly over rate their performance. They cannot take responsibility for their problems, it is always someone else's fault. They cannot accept their limitations.
Like in this murder, MM made many amateur mistakes. He based the cover up on movies and books, with no understanding of how LE really works.