BOSTON (AP) – More than two decades ago, Frank Enwonwu got caught smuggling five ounces of heroin into the United States from his homeland in Nigeria. He admitted his mistake and readily agreed to work as an informant, believing the U.S. had promised to keep him safe.

He went on to pursue his share of the American dream, driving a cab and training as a nurse’s aide – until a change in law in 1996 retroactively made him liable to be deported for his drug conviction, despite his work to help the government.

Now, he weeps in a room at a homeless shelter he shares with his 13-year-old son, fearful that any day he could be sent back to Nigeria to be tortured or killed as drug dealers with long memories seek retribution for his work as an informant.

“Trust me, no one there has forgotten what I did – even after 22 years. I’ll be killed there before I even have the ability to see daylight,” he said.

Enwonwu, 58, has spent about five of the last 11 years in detention while fighting his deportation order. His legal appeals all but exhausted, he now is asking to be spared on humanitarian grounds.

“I have a little boy who did not grow up with me because of all the time I have spent in detention. He needs me,” said Enwonwu, who is separated from his wife and has custody of the teen.

Enwonwu is under a final deportation order and could be taken into custody and deported without notice.

“This is a man who assisted the United States government as an informant, helping them prosecute drug-related crimes, and in so doing, he has put his life at complete risk. We believe that creates an obligation on the part of the United States to protect him,” said Meetali Jain, an attorney at the American University Washington College of Law International Human Rights Law Clinic.

Enwonwu admits he committed a crime when he brought drugs into the United States, but claims he was tricked by a Nigerian military officer who offered to buy him a plane ticket if he would show the man around Boston, where he had attended Tufts University in the 1970s.

The night of their flight, Enwonwu said, other military officers ordered him to carry two packets of heroin. He was arrested at Boston’s Logan International Airport after Customs officials found the drug.

Within hours of his arrest, Enwonwu said, federal drug agents asked him to participate in a sting to catch the dealers who were to come to Boston from New York to pick up the heroin. Enwonwu agreed, and two men were arrested. Their boss in Ohio was also prosecuted. All three were from Nigeria.

In the mid-1980s, Nigeria had become a major transit point for Asian heroin and South American cocaine being smuggled to Europe and North America. The transit networks expanded and became highly organized, prompting U.S. pressure on Nigerian authorities to crack down on the trade, which Nigerian police say frequently involves gang killings.

Enwonwu worked for the Drug Enforcement Administration for 10 months, providing the names of suspected drug dealers in Nigeria who U.S. officials believed were running drugs to the United States themselves or through couriers. He also supplied the names of Nigerians living in the United States who he had learned were involved with drugs.

Enwonwu said the DEA promised him he would not be deported and would be protected from the drug dealers he had ratted on.

“They knew how dangerous the drug lords in Nigeria were and they told me I wasn’t going back to Nigeria,” Enwonwu said. “Based on that promise, I continued my cooperation with them.”

The DEA acknowledges it paid him $1,600 for his work as an informant, but Herbert Lemon Jr., the DEA agent who Enwonwu claims made the promises, said he never told Enwonwu he would not be deported.

“Absolutely not. I (didn’t) have the authority to do it,” Lemon, who is now retired from the DEA, told The Associated Press. “That just didn’t happen.”

Lemon said he did tell federal prosecutors that Enwonwu had cooperated, which the agent believes spared Enwonwu from serving jail time. He got a suspended sentence and probation on the heroin charge.

“I think that’s the benefit he received for his helping the government,” Lemon said.

Lemon said he feels badly for Enwonwu’s wife and son who may be left behind in the United States, but said he does not fault the U.S. government for now moving to deport Enwonwu.

“He committed a criminal act, and as such, he has to face the consequences,” he said.

Enwonwu came close to being spared deportation in 2005, when U.S. District Judge William Young found the government had a “constitutional duty” to protect Enwonwu.

“The Constitution simply cannot permit (the government) to endanger the life of an alien, promise to protect him, and then cast him aside like refuse when he is no longer useful,” Young wrote.

However, Young was unable to issue a ruling in the case because a federal law, the REAL ID Act, made it more difficult for immigrants to get amnesty and also stripped federal district courts of jurisdiction in deportation cases.

Since that ruling, repeated efforts to have Enwonwu’s deportation order reversed by a federal appeals court have failed.

Enwonwu claims that while working for the DEA, he also worked as an informant for the Immigration and Naturalization Service, the predecessor agency to Immigration and Customs Enforcement.

Paula Grenier, a spokeswoman for ICE, declined to comment on Enwonwu’s appeal or his claim that he worked for ICE.

“The case has been presented to both administrative and judicial courts, and the matter has been decided upon by a judge,” Grenier said. “The next step in his case is his removal from the U.S.”