Lucas Decia was in the brutal crime scene when Alexander Villaluna, stabbed his former partner Jovi Pilapil and her new date Keith Collins in Kangnam BBQ in Westfield Hornsby in March 30, 2016.
Ms Pilapil was stabbed a couple of times by Villaluna and was limped away to a shop upstairs. Mr Decia followed her to make sure nothing else happened.
Mr Decia and Peter Dimbrowsky, a tradesman working in the shop where Ms Pilapil fled confronted Villaluna until police came into the scene.
SBS Korean program has more.