It is an odd experience live-tweeting a mass murder trial, as I have been doing for the past couple of days in Norway it's tough to get the hang of it.

You have to consciously divide your brain into different yet simultaneously working parts, as I'm told drummers and fighter-jet pilots do: listen with half an ear watch with half an eye process what you're hearing and seeing into tiny tweet-sized bites tap them super quickly into Twitter and send, while listening, watching and processing without pause. At the same time, take written notes that will become a TV script and lend coherent direction to live reports during court breaks.

Somewhere in the midst of it you've got to sit back and form some sort of analytical overview of where the legal argument is going, look around the courtroom and get a sense of how relatives and survivors, psychiatrists, lawyers and judges are reacting to events.

Just for a second here and there, you steal a glance of the man himself, responsible for Norway's largest peacetime tragedy, the biggest single massacre carried out by a lone attacker anywhere ever, and wonder just how on earth he could have done it. 

Not to mention, why?

Anders Behring Breivik is the most sinister, cold, and apparently soulless man that I have ever encountered, and I've met some with far more blood on their hands. 

The eyes are small, dark, empty specks. An enormous forehead, combed wisps of blond hair and pale skin shine ghostly white in the fluorescent courtroom. The black suit has a touch of the undertaker about it the pencilled beard screams narcissist attention-seeker. 

From time to time, Breivik's thin lips slide into a mocking grin. It's just inappropriate, callous, and wrong that he should find anything amusing. 

But on Wednesday, Breivik's demeanour changed somewhat, and the cocky veneer slipped. 

He was challenged and became grumpy. His story was reduced, bit by bit, by relentless questioning. He began to look silly. Then he got angry.

Despite myself, I felt deep satisfaction at his outburst - "Don't ridicule me!" - as the prosecutor plucked and teased and chipped away at his grandiose and quite possibly imaginary self-image. In that instant he was childlike, which is ironic since he'd complained about being spoken to like a child the day before.

I'd had a similarly visceral feeling - disgust - on Tuesday, when Breivik explained how the kids on Utoeya island had deserved to die.

"These were not innocent children," he said. They were a political youth movement "similar to the Hitler youth" and Utoeya was "an indoctrination camp".

I have no idea whether he is sane or not. Nor am I surprised that two sets of court-appointed psychiatrists have reached opposite conclusions. 

People kill people all the time, for all sorts of reasons or for no reason at all. Why should Breivik necessarily be mad, as popular opinion insists he must be? A fantasist of the internet age he may turn out to be, but that alone does not make him a lunatic.

It will take more than a few days to find out. He's intelligent, lucid, convincing and deeply sure of himself. 

On Wednesday afternoon Breivik came back from the lunch break fighting, calling Norway's maximum 21-year prison sentence "pathetic" and even saying he would "respect" a death sentence more. 

The mask has not fallen completely. Not just yet.

But here's one really good thing I experienced over the past few days:

A young woman who'd been in court, a survivor of Utoeya named Ida, thinks she's seen through the mask.

And Ida told me she wasn't afraid of Breivik anymore.