Well, Harry (Dresden) needs a thing from the victim to his tracking spells too. 

Actually he doesn't, if there is no scent article, he will look for any human scent/person in the area.
With an uncontaminated scent article, he will find that person and only that person ignoring others who might be in the area.

  I'd say because it's siblings and perhaps itself had been on the island before, perhaps in an attempt to free it's siblings or others from jail.  It may have been when it's siblings were captured by the Warden of that time, and put in the "minimum" security prison as POWs perhaps?  And maybe just a wild guess, the so called "British Prisoner," also dates back to that time?

It may be though that you can do it if you body swap a Starborn, but you have to have one available to Bodyswap and the new batch wouldn’t be born for nearly a decade after his last reported death. The only known surviving Starborn from a previous sequence is Drakul. Good luck trying to steal his body, especially with the White Council baying for your blood

I don't think a body would do Kemmler or anybody any good.  A body is a body, there is more to being a starborn than that I think.  The skills don't carry over, remember Luccio in a new body, she still was a wizard, but she lost the skill to forge Warden's swords to match the skills and talents of the Warden wielding it.  If it were as simple as switching out a body, you'd think the Corpsetaker would have latched on to one long ago for a chance to be starborn.

This brings to mind the Norse Berserker. And in the rages he means to use magic to kill, something that Lea tells up that Justin was attempting to teach him.

Maybe that is what he was meant to be, but it hasn't exactly worked out that way.  Yes, he went a bit berserk when Murphy was killed, but he was stopped before he could kill anybody.  Were he really in the mold of a magical Norse Berserker, he wouldn't have been stopped.  As soon as he felt the pain of the burn and smelled the sulfer, he came back to his senses and felt remorse, that doesn't happen with a true Berserker.  I think it is because of Malcolm's genes, and Margaret knew that would be the case as well. 

Do you have a picture of him in a hat?

 It's been rumored, but like Harry Dresden there are only pictures of him wearing a hat.  Harry won't wear a hat, but he does wear a harness and bell when he is looking for people.  He is an expert in "nose" magic, he can find someone on the wind who are hiding a half mile away.

  Or using the Star Wars metaphor, "One must not give into the dark side of the Force."  That is why a Jedi has to keep his or her emotions under control and not be too connected emotionally to anyone.
They have great power, but if they lose their temper and really cut loose with it, they start going
down a dark road and turn into someone like Darth Vader.

The lack of a tail hides his Malk heritage whereas his large size and slow aging (Mister is 18) do not.

Being 18 doesn't prove anything, the last few cats who have consented to share my space have lived to eighteen and beyond fairly hail and hearty, mice, rats, and birds, beware.. I have friends with 20 year old cats, Harry does mention that Mister is beginning to show his age..

Harry did not ask BOB (or Bonnie) about what being an starborn meant. They are literally a source of knowledge, and he did not ask. He did not ask Eb either. And yes, he asked LTW and Bigfoot but that was only in PT/BG, when he was aware of him being a starborn for many years before. He could ask Mac too.

Harry has only known about it the last few years, and he has been mostly dead or very busy all of that time.  Bob has been with Butters the last few years and Bonnie thinks milk is alive and cannot get her pancake recipes organized yet.  Eb so much as told him in Peace Talks that he wasn't going to tell him, he wasn't allowed to tell him. 

He did not ask Gray more about Margaret either. In fact, I do not think he even asked Thomas how Margaret was before she left Raith.

He might be afraid of what he finds out.  He has a picture of her that he is holding close..
I think now that he realizes being a star born is rather important, and Eb did tell him some things, I think he will find out more as the story progresses.

What I mean about Harry being a detective is not that he had the ways to find answers but that he should be naturally curious, as a professional trait.

But it is one thing to be curious, which Harry is, and obsessed, which he really doesn't have time for.