Today, in the fourth episode of "A Nation at Gunpoint," we look into the so-called "gun show loophole"-- by which anyone can buy a gun from a private dealer without a background check and no questions asked.

This was the long queue of people waiting to enter the Dulles Expo and Conference Center in the US state of Virginia.

It was the location for a large-scale gun show on the first day of 2016. All kinds of military and police goods, apart from automatic arms, could be bought there, including pistols, rifles and flak jackets.

According to the US Department of Justice, some 5-thousand gun shows take place around the country every year. And thousands of guns could be sold at a show during a weekend.

However, only one fifth of US states require a background check for all deals at a gun show. There's no such a requirement in Virginia.

Our CCTV reporter went to the show and asked a private dealer:

"You could be somebody who has a felony conviction, who has been convicted of domestic violence, who is a fugitive from the law, who is in the country illegally. If you are one of these catigories, in many states you can buy a gun from a private seller without going through a background check. That's a big loophole, and it's something that a lot of policy makers and advocates really put a lot of focus on closing," said Professor Kristin Goss, co-author of "The Gun Debate".

In fact, the Bureau of Alcohol, Tobacco, Firearms and Explosives reports that private sellers at gun shows are a major source of gun crime in the US.

The Bureau is in charge of tracing firearms. It said around 90 percent of firearms used in crimes have been re-sold at least once, often several times, before making their way into the hands of criminals.

So strengthening gun background checks is a pressing need for US President Barack Obama, who has been pushing for stricter gun control.

But not everyone welcomed the president's new executive actions when they were announced in January.

"I think it's half measured. it ignored or avoided the obvious which is chasing down convicted fellow and illegal possessor of guns in our streets. they are doing the great harm everyday. We have people in America who are rubbing all above with guns, coming in with a gun and we see it on the news every night, we should be moving to more aggressive prosecution to these people, because they are dangerous to us. So I was a proponent more aggressive using those status which are already on the books, the president was silent on that," said Ronald Hosko, fmr assistant director of FBA Criminal Investigative Division.

More than 30-thousand Americans are killed by gunshots every year. Some two-thirds of these were the result of suicide. More and more people are calling on the government to pay more attention to mental health problems. Tomorrow, in our next episode of "A Nation at Gunpoint", we'll look at where the resistance is coming from.