I seriously doubt this doctor is the sk. It ain't him. I'm sure I would fumble over words in a news interview too. Plus, he must be experiencing some level of embarrassment to even be remotely involved in such a heinous case.
But!
The call happened last May before media attention and way before the discovery of bodies. Apparently the sk used a throw away cell phone when the mother was called. How else could the doctor confidently deny making the call to the Shannon's family and LE? I'm sure the mother saved the phone number from the doctor and I'm sure LE traced it and it didn't lead to the doctor otherwise he would be proven to be a liar or somebody from his house made the call.
You see, I attempted after the "But!" to explore the angle of him being the sk but my train of thought got side - swiped. I guess it boils down to: Why would the doctor if he is the sk call the mother and give his real name and tell a lie that Shannon was with him and he helps people like her and then deny it when personally confronted? He didn't put Shannon on Gilgo beach as far as we know which eliminates any concern of his in terms of finding her, so why would he authentically make such a call?
Forget about it being the doctor. It was the sk who made the call just to mess with people and we know that he is not above behaving like that. There wasn't even a need for the sk to do such a thing other than manipulate, taunt and cause pain to loved ones.
What a wicked SOB!