No, this is offensive now. Most people during the Troubles didn't go out looking to kill someone because of their skin colour.
It's not 'linked to racial prejudice' (that stems from white oppression, in the US, in Europe, wherever) it is RACIST.
If you're still trying to justify his actions at the time, or feel you need to look into his eyes to decide if he's wrong, you are denying his racism.
He wasn't out for revenge (trying to find the rapist) he wanted to kill anyone who was black. This is a racist hate crime. He didn't apologise for that. He had a duty, if was going to launch this story, to make that very clear. He didn't.
If you're not offended, if you're trying to find excuses, if you're admitting his bravery or change of heart -you have a problem.