Burhan Hassan was lured from his Minneapolis home in November 2008 to fight a jihad in his native Somalia. After finding reality did not measure up to his handler's promises, he decided to try to make his way back home.

He was shot and killed a year ago - on June 5, 2009 - before he could escape. Relatives believe he was betrayed by the very people who persuaded him to join Al-Shabaab, a Somali terrorist group affiliated with Al Qaeda.

Now, law enforcement officials appear increasingly concerned Al-Shabaab members are trying to come back to America. But these members aren't disenchanted young men like Hassan, seeking to escape the terrorists' hold. Rather, the concern is that they are returning either to recruit more members or perhaps to plot attacks here.

That anxiety was displayed last Sunday, when an Aeromexico flight from Paris to Mexico City was diverted to Montreal. American officials learned that the plane carried Abdirahman Ali Gaal, who is on the no-fly list and is suspected of having links to Al-Shabaab. Authorities didn't want his flight traveling over American air space.

He was arrested after the plane landed and turned over to U.S. Department of Homeland Security (DHS) officials two days later. In an interview with Canada's National Post newspaper from the Plattsburgh, N.Y. jail where he is being held, Gaal said FBI agents asked about Al-Shabaab when they questioned him two weeks earlier in Mauritania. He denies any connection to the group.

But the FBI agents asked him about his ties to several Canadian men, including one who was reportedly killed in Somalia while fighting for Al-Shabaab.

Gaal admits that he had submitted a false refugee claim in Canada in 2008. In it, he claimed to be escaping the conflict in Somalia even though he was actually a legal resident of the United States.

His arrest comes after the Department of Homeland Security (DHS) issued an alert to police and sheriff's deputies in Houston last month urging them to be on the lookout for a Somali man. He was allegedly connected to Al-Shabaab and was believed to be in Mexico preparing to illegally cross into the United States.

The concerns are legitimate, and may not be fully appreciated, said Osman Ahmed, uncle of the slain Al-Shabaab recruit Burhan Hassan.

"There is a big concern from the Somali-American community about people getting training from Al-Shabaab and coming back to harm us," Ahmed warned in a recent interview with the Investigative Project on Terrorism. But the United States government "minimizes" and "understates" the seriousness of these threats, he said.

Nearly two dozen people have been indicted in cases related to Al-Shabaab recruitment in America.

Other prosecutions allege Somali smuggling operations involving Al Shabaab and other terrorist groups. That includes the recent indictment of Ahmed Muhammed Dhakane, a citizen of Somalia, on two counts of perjury in connection with his making false statements concerning his ties with al-Barakat and Al-Ittihad Al-Islami (AIAI) - both specially designated global terrorists.

According to the indictment, Dhukane failed to disclose that from June 2006 until March 2008, he lived in Brazil where he participated in and eventually ran a large-scale human smuggling enterprise. Prosecutors say that several of the individuals he allegedly smuggled into the United States were affiliated with AIAI.

Another case involves the federal prosecution of Anthony Joseph Tracy, who is charged with running a visa-fraud ring in conjunction with the Cuban Embassy in Kenya that enabled 272 Somalis to illegally enter the United States between May and December 2009. According to an affidavit filed in U.S. District Court, Tracy admitted his involvement in the fraudulent-visa ring. He said he was approached by Al-Shabaab, but denied cooperating with the group.

Most of the people Tracy is alleged to have helped smuggle into the U.S. remain at large, and Homeland Security officials cannot say whether they are affiliated with jihadist organizations.

Al-Shabaab represents a "threat to the whole nation, all of the world," Ahmed told the IPT. "Everywhere they could recruit somebody they will try – Europe, North America, Australia, Africa…And they want to disrupt world peace."

Ahmed warned that Al-Shabaab's main focus in recruiting Somali-American youths is not getting more soldiers to fight in Somalia's civil war. Many of them do not speak Somali and know virtually nothing about Somalia, he said. Somali Americans have U.S. passports, though, making it possible for them to travel back and forth to the United States. He believes that some day, these kids will return to America in order to "harm us."