you're a coward who wouldn't help
And you're a liar, who still hasn't actually paid attention to what I've written.
But by all means keep saying whatever it is that makes you feel better about yourself, even if it's at the expense of others by lying about them.
As a qualified first aider, my response as described here previously, is an accurate and responsible response based on the guidelines of the St Johns Ambulance, the UK's leading first aid trainers. Do no harm and do not do anything that puts yourself in danger as one casualty is always better than two. You're on a busy road, traffic in both directions, a serious crime, potentially murder, has just been committed. The responsible thing is to stand clear, stop traffic if possible, and call the emergency services. By all means jump in both feet first without thinking, trying to act like a hero - but I'll do what the best practices I've been taught and tested on dictate I should.
I have had cause to use my first aid skills in the past, and I would do so again. If you really feel the need to divulge whatever action you've taken in the past to try and justify your outrage, go ahead. Personally, I consider that in extreme bad taste and smacks more than a little of chest-thumping.