I wouldn't trust them - the murder and robbery rates, far lower in jurisdictions where dangerous weapons are controlled, say it all.
In the case of the USA, that's not really accurate, because "control" is on a state by state basis. Take a look at Illinois. Chicago is rife with homicides by firearm. Illinois has some of the strictest gun laws and regs in the country but some of the worst gun violence in the country. If you're a criminal living in Chicago, the solution is simple: go to another state where you can easily obtain one. And then there are the gun shows. No federal regulation requiring them to run background checks. This means that a raging homicidal maniac can walk into a gun show, point to an AK-47 and walk out with it.....legally. If you want "control", the control needs to be nationwide, not just in the state you live in. The police can keep catching criminals and seizing their weapons but it's like a fish tank with a hole in the bottom, placed underneath a running faucet...as the water runs out the bottom, more water keeps on coming in from the top.
Take a look at this article:
"According to the most recent available gun trace data from the Bureau of Alcohol, Tobacco, Firearms and Explosives, the percentage of out-of-state guns used in crimes in New York City has been increasing in recent years. In 2009, 85 percent of crime guns came from out-of-state. In 2010, that proportion was 86 percent, and in 2011, 90 percent of crime guns came from outside the State of New York."
New York has very strict gun regulations, on par with Illinois, yet, as the article states, 90 percent of crime guns in 2011 came from outside the state of new york.
Whether you're arguing that guns are good or bad or whatever, laws and regulations on guns must be universal in the USA before we can truly see if gun restrictions have any effect. Common sense might say that it most certainly would have an effect but as long as criminals have planes, trains, and automobiles and can cross state lines at will to obtain firearms, we really don't have any statistics yet to make such a claim.