"Handguns Are Used in Most U.S. Assaults and Robberies," reports a BBC caption; the article elaborates: "Handguns are used in two-thirds of robberies and assaults...according to statistics from the Federal Bureau of Investigations."
Uh, no: according to the Justice Department's National Crime Victimization Survey (2005 data), table 66, handguns are used in 5.4 percent of U.S. assaults and 26.3 percent of robberies.
Even if one uses the FBI's Uniform Crime Reports data, which is generally thought to be less reliable because it focuses only on crimes reported to the police, only 42.2 percent of all robberies involved firearms generally (likely nearly all handguns, but still not "most" robberies), and only 21.9 percent of all aggravated assaults involved firearms generally, even though "aggravated assault" is a kind of assault that is especially likely to use a deadly weapon -- the statistics for all assaults would surely be far lower. (I cite 2006 data here, but the 2003 data is comparable.)
Or check out the L.A. Times, which reports that "[D.C. Officials] argue handguns are involved in most violent crime." But the NCVS data reports that handguns are used in fewer than 8 percent of all crimes of violence. This doesn't include homicide, but homicides are fewer than 0.5 percent of all crimes of violence, so even if one includes homicides the answer would be about 8 percent.
Here's my guess about what happened: The petition does say that "handguns are the weapon most likely to be used in a street crime," a statistic that the NCVS supports. According to NCVS, handguns account for a plurality (roughly 1/3) of weapons used in the about 25 percent of violent crimes that the victims believed were committed with weapons (as opposed to hands and fists), which is more than any other class of weapons. The petition's statement is thus accurate, though not terribly helpful and potentially misleading. But this then got transposed into the off-by-a-factor-of-6 L.A. Times statement that "[D.C. officials] argue handguns are involved in most violent crime."
Now I should stress that handguns are indeed involved in many crimes, and the majority of homicides. I oppose handgun bans because I think they do more harm than good, but I certainly don't want to pooh-pooh the harm done by criminals with handguns. But these stories help show how skeptical one should be of media reporting about statistics (and likely about other things as well).