Livonia, Michigan (CNN) -- U.S. authorities had another Nigerian-born man with an engineering background on their radar when Northwest Airlines Flight 253 prepared to land in Detroit, Michigan, on Christmas Day.

Emmanuel Chukwu shared the same travel itinerary with Umar Farouk AbdulMutallab, the suspect in the unsuccessful attempt to blow up the Amsterdam, Netherlands-to-Detroit flight. Both men were originally from Nigeria and had studied as engineers.

But while the 23-year-old AbdulMutallab was a loner and a global nomad whose family tried to warn U.S. authorities about his turn toward Islamic extremism, Chukwu -- a 41-year-old naturalized U.S. citizen and father of four American children -- also caught the attention of government officials.

Federal agents pulled Chukwu aside for several hours of intense screening when Northwest 253 landed in Detroit, shortly after authorities say AbdulMutallab tried to set off an explosive device concealed in his underwear. Chukwu said agents told him his similar background prompted the additional scrutiny.

"The FBI came back and said, 'You know what, it's a very unfortunate coincidence, right, that the suspect is a Nigerian,' " he told CNN. "And that was the first time I got to know that the suspect is a Nigerian and happened to be an engineer like myself."

But unbeknownst to Chukwu, CNN has learned, he was being tracked in TECS -- a massive government database accessed daily by law enforcement agencies. The database, dating back to the 1970s, allows government agencies to compare watch lists with flight manifests and to look for red flags that could prompt a secondary screening.

"TECS really is the backbone or the mainframe, the real operating system for Customs and Border Protection that has the information from other law enforcement agencies," said Kathy Kraninger, a former Homeland Security official and now a security consultant. Kraninger said that while some of the information housed on TECS is benign, most of it is "derogatory," ranging from immigration and customs violations to warrants and criminal records.

On December 25, Chukwu was seated about five rows behind AbdulMutallab when the bombing attempt took place.

"People started screaming, 'Oh, there's smoke, there's smoke,' " Chukwu said. Once the plane landed, he said, "I just said, 'God, thank you, I'm alive.' "

Chukwu said he has flown between Nigeria and the United States "about 20 times or more" since 1995. But in addition to being patted down and searched during his secondary screening, Chukwu said, he was questioned well beyond his frequent travels to his homeland.

Some of the questioning involved an incident from September 26, 2008, when he was caught in Amsterdam carrying an unloaded shotgun in his checked luggage on his way from the United States to Nigeria.

He said Dutch authorities told him, " 'Oh, you have a gun in your bag.' I said, 'Yes, I know, I have a gun in my bag,' It's an unloaded gun, brand new, never been used,' " Chukwu said.

But both the Netherlands and Nigeria forbid civilians to carry a gun without permission. Dutch authorities confirmed the 2008 incident and said Chukwu was released and given a two-year probation.

It's unclear whether a record of the gun incident or other risk factors -- Chukwu's travel patterns and personal profile -- triggered his secondary screening in Detroit. The Department of Homeland Security will not comment on the matter.

But for Chukwu's pregnant wife, Janefrances, the additional screening meant six hours of waiting on Christmas Day -- not knowing if her husband was coming home.

"On the 25th, four children would have lost their dad," she said. "What I know is that my husband is not going to harm anybody, has never harmed anybody. I hope that they will put the right people in the database so that they will be able to catch the people who will cause harm to the United States."