Working across international borders to clamp down on sex abuse is no easy task, especially when it involves young children. But as a U.S. official told CNN's Richard Quest, it's a task that's made easier with the help of the public.

In the past eight years, the United States has prosecuted 90 pedophiles who went overseas to abuse children. John Morton, the director of the U.S. Immigration and Customs Enforcement, says discovering these criminals is hard work because it involves tracking people who are doing everything they can to keep a secret and also means working with a local police force in a foreign nation.

He said that most of the tips in these cases come from the public.

"We don't generate the vast majority of the leads in these cases," he told CNN. "We get them from non-governmental organizations, from people who are paying attention on an airplane and notice that a child is traveling with someone that they really shouldn't be traveling with, who see something amiss and report it to authorities or to a group that specializes ... in this kind of work. And then we get involved."

The children are too scared or too young to report the crime, so it is vital that if someone suspects something suspicious, they need to report it.

"We are not talking about some ordinary crime. We are talking about the assault and abuse of small children, as young as three or four years of age, usually in circumstances of grinding poverty, very difficult cultural conditions," he said. "And if they don't speak up, chances are the crime is going to go uncovered and that child's life is ruined. They need to say something. They need to allow us to get in there and investigate and put these people away.

"We all have to stand up and vindicate those children, because they can't stand up for themselves," he added.