Now don't get me wrong here, no doubt this guy will be proven to be guilty - after all, the majority of these attacks are indeed domestics. But, reading through that article it seems that the evidence so far revealed seems pretty scant to me.
- he was in a relationship with someone else (not great, but doesn't typically lead to murder in the vast majority of circumstances)
- he stood to benefit financially if his partner died (as would the vast majority of people)
- there was a spirit level left outside which he allegedly left there to fake a burglary (um, I'd do a little more than that if I was faking a burglary)
- he took the front off the cat flap the same day (perhaps he was faking a forced entry by a cat burglar?)
- the police thought he was behaving oddly and "one of the officers mouthed the word 'domestic' to his sergeant, who nodded in agreement." (well gosh, let's just lock him up here and now, why bother with a judge?)
As an aside, he also suffered injuries to his back in trying to (allegedly) protect his partner and his explanation of events would have, as the prosectuor notes, "superficial attraction to the uninformed", i.e. it looked like he may well have been trying to defend her.
Like I said, he may well be guilty, but it doesn't seem that compelling a case so far.