I had provided a lengthy, multi-citation response, that has, unfortunately, been eaten by the internet gremlins, so, alas, I will simply respond to this:
No. Once again you shamelssly take my words out of context. You do it with such increasing frequency, one might suspect you incapable of establishing firm reasoning to support your sweeping gun control argument.
Nanny-Nanny, boo-boo!
I have provided detailed analysis, with citations, for every argument I have made. The same cannot be said of the responses. It was not I who initiated this thread with an irrelevancy, or who dragged it off topic. I provided responses to comments made. Simply because it is a relatively simple matter to demonstrate, with statistics, with counter-examples, with the weight of data, the application of logic, etc., etc., etc., that the fundamental arguments put forth in support of paranoid fantasies of unfettered gun carriage are as gossamer as the wings of a butterfly and of less substance does not warrant such chagrin. I'm sorry you have nothing to fight
with.

The reality is that there is a vanishingly small chance that anyone carrying a firearm will be on the scene when a crime occurs, as happened in the original post. How unlikely? About the same as winning a multi-million dollar lottery. I get all wonky about this below, but the short answer is that with only 8 million concealed-carry permits in the country, despite the huge numbers of firearms, the chance of anyone being armed in any location is less than 1%, and even less likely that they will be in the vicinity of a crime (the average armed crime occurs in well under a minute). Moreover, armed citizens are far more likely to be shot and killed than unarmed ones. One study (in Philadelphia, over a 3 year period) found that someone carrying a firearm was more than 4 times as likely to be shot, or killed, if armed, than a similarly-situated unarmed citizen.
Carrying a gun increases risk of getting shot and killed Overall, Branas's study found that people who carried guns were 4.5 times as likely to be shot and 4.2 times as likely to get killed compared with unarmed citizens. When the team looked at shootings in which victims had a chance to defend themselves, their odds of getting shot were even higher.
What this points out is the frustration I have always had with gun-ideologues. It is not about rationality, it is not about statistics, it is not about logic, or analysis, it is about a die-hard conformity to an ideology and an adherence to a mindset that is based upon a fantasy. It's about feeling a certain way.
Now, the wonky bit:
I am not an actuary, or a statistical whiz, but I can do basic math, and I am pretty good with formal logic. There are approximately 300 million privately-owned firearms in the United States, and about 340 million residents.
U.S. most armed country with 90 guns per 100 people However, since fewer than half of all households in the United States have firearms in them, and continues to decline, the distribution of firearms within the population is seriously uneven.
Gun violence in the United States - Wikipedia (In 2004, 36.5% of Americans reported having a gun in their home[.]);
Share of Homes With Guns Shows 4-Decade Decline It is estimated that the average firearm owner owns between 6 and 9 firearms. Since I technically only own two, someone is really making up the difference....
Handguns make between 25% to a half of the total of firearms in the United States. Approximately 65 million. (I note this, because only handguns are routinely used for carriage). "With hard numbers or estimates from all but three of the 49 states that have laws allowing for issuance of carry permits, the GAO reports that there were about 8 million active permits in the United States as of December 31, 2011."
Concealed carry in the United States - Wikipedia Texas has one of the highest percentages of gun carriage permits in the country - but only about
1.8%. By one estimate, "On an average day, more than a million Americans are carrying guns outside their workplace."
The "Facts" About Handguns (not vouching for the estimate, just reporting it). Of course, not everyone with a permit carries their handgun all the time. In fact, most report they keep them in their cars more often than on their person. (Lost citation.)
So, on an average day, only .3% of the population is "carrying" a firearm, and only .15% of the time are they actively armed (as opposed to carrying it in the glove box). Since the average crime last less than a minute, and they would have to be "on scene" at that particular moment in time, and prepared to respond (it is pointed out in the Branas study above, that more often than not, the victim cannot respond before violence is done to them - the bad guy already has the drop on them). Combining those factors and probabilities, having that combination of factors is, statistically, less than a .02% chance, and probably even less than that.
Can it happen? Of course it can, that's why it makes the news - of only locally, and if only on page 3.