A grand jury indictment unsealed in federal court Tuesday charges 24 people - most naturalized U.S. citizens of Vietnamese descent - with several federal law violations in connection with "a sophisticated marriage fraud scheme by evading U.S. immigration laws," the U.S. Attorney's Office said in a news release.

Twenty-one people, ranging in age from 29 to 56, were arrested and booked into the Salt Lake County jail without bail on Monday. Three of the people charged have not been arrested. Federal agents on Monday searched for people at their homes and businesses and collected computers and boxes of documents as evidence.

Those arrested are charged with conspiracy to defraud the United States, alien smuggling, marriage fraud, aggravated identity theft and visa fraud, according to the indictment. They each face up to 32 years in jail.

Details on the 18-month investigation called Operation Morning Glory were released Tuesday during a news conference at the U.S. Attorney's Office. The investigation started with a tip by a citizen to U.S. Sen. Orrin Hatch's office in 2004. The agencies involved in the investigation were the U.S. Attorney's Office, Immigration and Customs Enforcement, State Department Bureau of Diplomatic Security and Citizenship and Immigration Service.

Investigators believe some of those charged recruited 80 to 100 Utahns to marry Vietnamese to help them get proper U.S. documentation. Men and women were equally involved in the fake marriages, investigators said.

In order to get through the U.S. immigration system, the couples were often coached well by those charged about what to say and what questions federal officials might ask. The people who were matched into couples would visit each other in the U.S. or Vietnam. During those visits, the couple would be photographed many times together in different changes of clothes to make it look like they were a longtime couple, investigators said.

Vietnamese nationals paid ring leaders up to $30,000 for the match. Ring leaders, who prepared much of the immigration paperwork, in turn paid Utahns $500 to $10,000 and travel expenses to agree to the fake marriages. Recruiters told Utahns the marriages were not "illegal" and they would be helping Vietnamese "escape a terrible situation," the news release said.

Charles DeMore, an Immigration and Customs Enforcement special agent, said the Utah scheme was a threat and danger to the United States because those arranging the fake marriages had no idea about the intentions of the Vietnamese nationals.

"These defendants left the door to our nation open . . . they put your national security at risk," he said.

Investigators said the federal government is looking into how the couples were able to get through the immigration system and plan to "refine" policies and procedures.

Investigators allege there were five ring leaders - Hoa Thanh Vo, 39; Henry Ngoc Nguyen, 45; Buu Ven Truong, 37; Ngoc Hoa "Noa, Nora, Norwa" Huynh, 33, and Danh Huy Do, 33. They said they are still deciding if those who were involved in the marriages will be charged.

On Tuesday, some businesses owned by those arrested were closed. Vo is involved in several businesses, including Vietlink Travel and Service and Nails Divine in a new strip mall on 3600 South near Redwood Road, according to state documents.

Hang Hoang, 40, Vo's wife, works at Nails Divine, which has stayed open. Vietlink Travel, however, is shut down because federal agents took much of the business's computers and documents.

Hoang, who moved from Vietnam to Utah 15 years ago, said the two married 13 years ago and have three children ages 12, nine and four. She said Vo was arrested at their West Valley City home on Monday and spoke to him by phone Tuesday.

jsanchez@sltrib.com