The criminal checks will access what they can - not helped by reducing intel sharing across the EU through Brexit. All possible checks are done on identity, history and reasons for travel - all visas/claims.
Asylum claimants are (or used to be, so I imagine he was) interviewed to assess the veracity of the claim and his own identity.
I can’t say what records Sudan keeps and/or shares, as it is a horrific warzone - but it is possible he did or did not commit crimes that we can’t 100% verify - I think it more likely this was the first of this type - but maybe I’m wrong - however, we can’t assume that everyone is just waiting to do this and has a long history we didn’t notice of doing it.
I am sure the whole application process will be rigorously checked for this case - then we may know more.
We do know it was a horrific attack, we know he’s in custody and we know will be dealt with through our legal system. I’m sure the HO will review the application and maybe there’s lessons, maybe not - we cannot know yet.
That’s enough surely - following the law and investigation into it all. We don’t need to rampage across the U.K. or decide all Sudanese (though it was Somalis earlier) should be evicted from the U.K.