For the second one there are to many variables to predict any one out come. If the shooter is inside the crowd then other armed people wouldn't be able to get a clean shot for awhile, also if he's inside the crowd. It's also possible(however unlikely) that people could just start shooting each other if everyone draws their guns. And if the shooter is on the outside of the crowd then an armed person might be near the outside and be able to quickly kill the original shooter. Or he might be on the inside and not be able to kill the original shooter before many people. Or the armed civilian could be on the inside and the original shooter could be on the outside but not be able to kill very many people before he himself is killed due to having poor marksmanship, people often think of guns as something that you can just pick up and easily hit what your aiming at and that when you do hit that person you will instantly kill them. When that is often not the case, especially with handguns even at a relatively short range(lets say 30 feet) an in-experienced shooter might not be able to hit many of the people he aims or only hit them in the arm and if the shooter firing into the crowd does hit someone in the chest or head it might not be in instant death. There have been cases where people have survived shots to the head at a range of just a few feet. So theres no way to predict how many people could die.

You're basically assuming that the average civilian is incompetent.

No it's a simple question of reaction time. I assume you're talking about the first scenario. So: Attacker stabs first person. No gunshot for people to register, if they cut the throat, heart or spinal cord then there wouldn't even be a yell, just one person dropping in a crowd. All that would take about one second. So, turn and repeat. The people next to you would notice, but wouldn't be able to run cos of the people around them. Considering it only takes a second to kill one person, I think you could make another 4 deaths before the stampede got under way. Very few people have the fight reaction, especially in crowds when everyone else has the flight reaction. So in the first 30 seconds of your attack you've already dropped 6 people and no ones trying to stop you. The lack of gunshot would stop people further away from knowing there was someone [i]to[/i] stop until people have cleared out a bit. Again, crowds move slowly. Even whilst running. Assuming the attacker doesn't go for the trampled people they would be able to catch and kill at least another 6 before anyone thought to try and stop them.

One person per second is not at all realistic unless the attacker has incredibly advanced training. The average person would likely require multiple strikes for each kill. Also, unless every single person is blind or the whole crowd is moving in the same direction with the attacker at the rear, then people are going to see the first person go down.

Not one person per second, one second per person. Granted, a few seconds moving between people, but one second to kill them. And I was only talking about the first person anyway. You don't need advanced training to force a knife through someone's skull. As for the first person being seen, granted. But someone collapses silently in a crowd your first thought isn't going to be "stabbing" it's going to be "trip" or "heart attack". Also you forget how much people ignore things they don't think are their problem.