The 17-year-old collected title after title in the cadet and junior ranks but had to settle for a silver medal at the Youth Oceania Boxing Championships in Samoa last month.
He has stepped up to the youth ranks this year and was beaten by Australian Jake Clauge in the gold medal match in the 60kg class.
Had he won the bout, Murdoch would have qualified for the Youth Olympics later this year in Argentina. Now his selection hangs in the balance.
He desperately wanted to win and put his loss down to some early hesitancy. His older brother, Shem Murdoch, had another theory. Kasib picked up a stomach bug while in Samoa and actually did well to get through the fight.
But the Kaikorai Valley College year 13 pupil did not mention that in the interview.
''I'm a wee bit disappointed with the end result. I really wanted that gold,'' he said.
''Still, it was a very good experience. The guy I lost to is a youth Commonwealth silver medallist.''
Clauge secured a unanimous decision.
''There wasn't heaps in it. He didn't smash me ... and I didn't feel like I was out of my depth or anything.
''I felt like I ended the fight well but I started too cautiously. I almost gave him too much respect when I should have been throwing those punches at the start.
''I didn't want to rush it. I was trying to find that fine line between being patient but still having a good work-rate, or being rushed and getting messy.''
The Youth Olympics are still a possibility ''but it is a lot smaller now because I sort of needed that gold medal''.
Murdoch understands New Zealand can take two fighters to the Youth Olympics and he may still get to go as no-one qualified automatically by picking up gold at the Oceania Championships.
Murdoch's next assignment is at the Australian Golden Gloves in August. He won the junior 60kg class at the tournament last year and hopes to add a youth title.
As a junior, Murdoch often fought youth competitors so he has not found the step up too daunting. The rounds are a minute longer but that does not faze him as he spends a lot of time working on his fitness and making sure he is in good shape.
Murdoch hopes Clauge will show up the Golden Gloves so he can avenge his loss.
