It will be fo the jury to assess whether the evidence you can give casts doubt on the whereabouts of your son at the material time. It's not necessary for alibi evidence to prove he did not do it; it's sufficient if it makes his presence at the scene markedly less likely and the jury not sure of guilt.The 'perfect' alibi is commonly the one which the jury distrust; it's just too good. And the prosecution always have to prove presence and the elements of the offence, beyond reasonable doubt;
That the victim knows your son and named him is unhelpful, but, even so, identification evidence is always subject to great scrutiny and a warning from the judge pointing out the difficulties it presents. We have all had the experience of 'recognising' someone we know and see somewhere, only to find that it's not them. Whether that is ever applicable in this case depends on the circumstances; obviously a clear sustained view of a 'friend' who then attacks another in the heat of an argument, say, is obviously a different matter on identification and has to be challenged on another basis (malice of victim, invention,self defence etc) as distinct from a very brief view, in difficult conditions and genuine mistake.
The problem with alibi is that, as the defendant maintains that he was elsewhere then it is not possible , or not easy, to run another defence with it. He can't say"I was not there but if, which is not admitted, I was then it was self-defence" ! If the jury finds him present but lying about it, they have the unchallenged account of the victim, with any embellishments and self-justification that may contain.