(a) It is most unlikely that Mr Murphy had had the time to learn that you had stabbed Regan before he came upon you trying to force your way, with a knife, into the maintenance shed, in which Barton had sought refuge from you.
(b) In cross-examination, you claimed that Mr Murphy said those words ("Fucking black, you killed Regan and I'm going to kill you") in a louder voice than he said the words which preceded them, namely "What the fuck are you doing here?" Yet Mr Barton, who was on the other side of the door of the shed, did hear you say words to the effect "What the fuck's going on here?" but did not say that he heard Murphy say "Fucking black, you killed Regan and I'm going to kill you."
(c) Significantly your counsel cross-examined Mr Barton in some detail. However he did not put to Mr Barton in cross-examination - as he would have been obliged to do if it was then part of his instructions from you - that Mr Murphy had said to you the words "Fucking black, you killed Regan and I'm going to kill you."