What would you do if you came across a dying man - stop to help or walk away? Last week Tara McCartney was caught up in a horrific attack on a bus. She was shocked by the response

The coverline to the story below stated wrongly that the author of the piece "was the only one" of the passengers who tried to help the fatally wounded man. As was made clear in the story itself, although the author recalled appealing for help without receiving assistance, a number of others also assisted at different points.

At first I thought it was some sort of domestic. It's hard to think back, everything happened in slow motion, but I think other people thought the same thing. I was on the lower deck of the number 43 bus on the Holloway Road at about 10pm when I heard a woman shouting, sort of screaming, saying, "Oh my God, what's he doing? Make him stop, make him stop."

I looked up and looked around me. The deck had been full, or had certainly felt full, when I got on at the Angel at around 9.30pm. It had thinned out a bit, but there were still plenty of people. Everyone heard her.

It was a weird thing to be saying if it really were a domestic tiff, but the way the woman was shouting was as if in disbelief. She didn't shout, "Help, help!" or anything like that. She shouted for a few moments then stopped. Then it started again, and then again. At that point I said out loud, "Oh my God, what's going on?"

By this point the bus had stopped at a bus stop. And while she was still shouting upstairs, this youngish black guy came down the stairs very slowly, sauntering down, exaggeratedly slowly, with this weird kind of vacant smile, almost a grin, on his face. He looked all around at everyone, wide eyed, before getting off. I was by the door, next to a window. He was moving so slowly, I made no connection between him and what was going on upstairs. Then a man came down and said to the driver: "You need to stop the bus, you need to stop the bus, there's someone being attacked." Then he got off the bus and disappeared. I don't know whether he has ever come forward to make a statement to the police.

At some point, the woman who had been screaming had come down the stairs. We found out later that she was the victim's girlfriend. White-faced, eyes like saucers, she was saying: "Did you see him? Did you see him? He stabbed him." She got off the bus, obviously in severe shock.

Then a couple of moments later the victim came down. He had blood on his shirt - not lots of it - but he was saying, "Look, he stabbed me, he stabbed me."

What do you do in that situation? I definitely hesitated - I was thinking: there's no way I'll be the first person to do something here, there are so many other people about. And then, suddenly, I had a very quick realisation that no one else was going to do anything. I put my bag down and went to get my phone. Then I went to the man and said, "Sit down," because he was sort of wheeling about, taking his shirt off and saying, "Look, look."

But as soon as he sat down he started to go a bit floppy. I kept looking round expecting other people to engage with him as well, but no one did. I was trying to call 999 on my phone, and I think he sat on one of the fold-down seats in the centre of the bus. He started to breathe a bit heavily. I wanted him to lie down because obviously he was wounded. Things started to happen quickly. I was calling 999 and trying to get him lying down at the same time. He was quite a big guy, not huge but an adult man, much bigger than me, and at that point I couldn't physically do both things at once, so I called out, "Can someone help me? Can someone help me?" Nothing happened. No one made eye contact. I couldn't quite believe it.

I took off my jumper and put it over where I thought the wound was, then tried to get him down on the floor. I kept saying, "Someone help me!" But no one did. I was on the phone to the emergency services and I suddenly realised that the operator had been saying - I don't know for how long - "Which service do you want? Which service do you want?" Two other girls called the emergency services, too; one was on the now stationary bus, the other was outside. The operator told me to pass the phone to the bus driver.

By the time I'd got the man lying down he very quickly started to go into shock; he was very pale and sweating. My jumper was over his stomach and I was trying to apply pressure, but because there wasn't blood rushing out I wasn't sure that that was doing any good.

He was in a position where his neck was craned round under a seat; the sensible thing would have been for someone to help me to move him to make him more comfortable, but no one did. All I could do was stay with him. I didn't want to move him around to see where he was hurt so I just had my hand under his head and was holding his hand with my other hand, saying, "Can you tell me your name?" That was the only thing he manage to slur: "Richard."

I don't have any real first-aid training, I've just absorbed things, mostly from the Girl Guides. But I do know you have to get a patient to stay with you and not fall into unconsciousness, which they will do if they are in shock. Reassure them, stay with them. So I said: "Can you tell me how old you are, where you live?" but he wasn't answering, he was just kind of rocking back and forth. The only other thing he said was, "I want to go to sleep." I kept saying: "No, no, you've got to stay with us." He was shaking by this point, sweat all over him. I kept saying to him: "It's fine, they'll be here any minute, it's just superficial, there's not much blood, you're going to be fine."

A young girl who had stayed on the bus grabbed his legs and pulled them up on the seat. She was the only one who physically did anything at all, this tiny girl, and then after a few moments the other girl who was still on the phone to the emergency services said: "Put his legs down, they say put his legs down."

I told her to take off her jacket and put it over him, which she did. But it was only a light little thing and it wasn't really doing anything. He was a full-size man. At one point this other guy came over. I'm not sure, but I think he got on the bus to have a look. He was leaning over, looking, and he was wearing a jacket, a proper jacket. So I said: "Can you give me your jacket so I can put it over him?" He just said "No". That was it.

By that point I think there was only Richard, two other girls, the driver and me left on the bus. There had been plenty of people on the lower deck but they just melted away. There was a bus full of people milling around outside. But it was as if no one wanted to get involved. A lot of people must have just gone.

The driver was in shock. When the police came the engine was still running. They told the driver to turn it off, and he said, "No, no, I've got to go back to the depot." They said, "The bus isn't going anywhere."

I find it astonishing that no one else approached an injured man in this situation. I suppose people might not have thought it was life-threatening. And I suppose some people might have been squeamish. But nevertheless, there was blood, and a guy injured, and you were there. You don't just leave him, and leave someone else to deal with it. Perhaps things wouldn't have happened any differently for him, but every bit of statement and every bit of evidence is going to be vital. After he'd been taken away in the ambulance, I kept saying, "Where did everyone go, why didn't anyone do anything?" I could understand if there had been any danger. It's always my reaction to move away or avoid anyone acting strangely or scarily. But it was clear that the person who had done it had long gone - because we all saw him go. There was no danger at all.

Eventually the police and paramedics came. There was blood splattered on the stairs and the floor but there wasn't that much of it. I remember thinking at the time that I must have blood on my clothes, and looked at myself. I was wearing a white T-shirt and I'd been kneeling with him but it was just my hands that were covered in his blood. I heard a girl say, as he was being taken away in the ambulance, that she hadn't wanted to give him any of her clothes. I said, "What, in case they got messy?" Her face said yes.

Of all the people who were on the bus, all of us potential witnesses in a murder trial, only five passengers, plus the driver, went to the police station to make statements. While we were there, at about 2am, one of the policemen said: "I'm sorry to have to tell you this, but he died." I was in floods of tears. None of us expected that. I learned later that the man's name was Richard Whelan, that he was 28 and that the incident that ended in his death started with a man throwing chips at his girlfriend.

I get the number 43 every day to go to work. Like a lot of people, I have been nervous to travel after the terrorist attacks, or certainly more aware. I have found myself looking at other passengers, especially if they were Asian, checking to see whether they were carrying a bag and so on, even though I knew it was ridiculous. But I have also found it strange, since July 7, to read reports about Londoners being stoical and helping each other. My experiences have not quite been like that. One morning, one man on my bus got into a rage because the driver had closed the doors before he was able to get off. Then, when he'd got off, a woman noticed a bag in the luggage area at the front. She yelled out, "Who's bag is this?" and a girl sitting next to the luggage rack said it was hers. And for some reason the woman flew into a rage, too. She was shouting, "Maybe you want to get blown up, but I don't!"

Earlier in the week, having seen reports about the murder in the papers, I got very upset. I decided to leave work and I really didn't want to take the 43 home. It would be the first time I'd followed the same route, and I was terrified of seeing the suspect again. So I started to walk towards the tube. Then I thought about the warnings that there might be a third terrorist attack. I eventually decided that I was more scared to get on the tube than I was to get on the bus. Of the two, that seemed to be the most dangerous. So I ended up back on the 43.

There is nothing special about me. I did what, until last week, I assumed anyone would do in that situation. But you simply don't know until it happens. No one helped me, but then I didn't get up and go to see what was happening on the top deck when the woman first screamed, when she was clearly desperate for help. I suspect I am the sort of person who, if someone had been acting strangely or scarily, would come downstairs and walk away.

· Tara McCartney is a pseudonym. She has not been paid for this article. If you have any information about this incident please call the Metropolitan police incident room on 020-8345 3985 or Crimestoppers on 0800 555111.