He was 17 when he came to New York from Hong Kong in 1992 with his parents and younger sister, eyeing the skyline like any newcomer. Fifteen years later, Hiu Lui Ng was a New Yorker: a computer engineer with a job in the Empire State Building, a house in Queens, a wife who is a United States citizen and two American-born sons.

    But when Mr. Ng, who had overstayed a visa years earlier, went to immigration headquarters in Manhattan last summer for his final interview for a green card, he was swept into immigration detention and shuttled through jails and detention centers in three New England states.

    In April, Mr. Ng began complaining of excruciating back pain. By mid-July, he could no longer walk or stand. And last Wednesday, two days after his 34th birthday, he died in the custody of Immigration and Customs Enforcement in a Rhode Island hospital, his spine fractured and his body riddled with cancer that had gone undiagnosed and untreated for months.

    On Tuesday, with an autopsy by the Rhode Island medical examiner under way, his lawyers demanded a criminal investigation in a letter to federal and state prosecutors in Rhode Island, Connecticut, Massachusetts and Vermont, and the Department of Homeland Security, which runs the detention system.

    Mr. Ng's death follows a succession of cases that have drawn Congressional scrutiny to complaints of inadequate medical care, human rights violations and a lack of oversight in immigration detention, a rapidly growing network of publicly and privately run jails where the government held more than 300,000 people in the last year while deciding whether to deport them.

    In federal court affidavits, Mr. Ng's lawyers contend that when he complained of severe pain that did not respond to analgesics, and grew too weak to walk or even stand to call his family from a detention pay phone, officials accused him of faking his condition. They denied him a wheelchair and refused pleas for an independent medical evaluation.

    Instead, the affidavits say, guards at the Donald W. Wyatt Detention Facility in Central Falls, R.I., dragged him from his bed on July 30, carried him in shackles to a car, bruising his arms and legs, and drove him two hours to a federal lockup in Hartford, where an immigration officer pressured him to withdraw all pending appeals of his case and accept deportation.

    "For this desperately sick, vulnerable person, this was torture," said Theodore N. Cox, one of Mr. Ng's lawyers, adding that they want to see a videotape of the transport made by guards.

    Immigration and detention officials would not discuss the case, saying the matter was under internal investigation. But in response to a relative of Mr. Ng's who had begged that he be checked for a spinal injury or fractures, the Wyatt detention center's director of nursing, Ben Candelaria, replied in a July 16 e-mail message that Mr. Ng was receiving appropriate care for "chronic back pain." He added, "We treat each and every detainee in our custody with the same high level of quality, professional care possible."

    Officials have given no explanation why they took Mr. Ng to Hartford and back on the same day. But the lawyers say the grueling July 30 trip appeared to be an effort to prove that Mr. Ng was faking illness, and possibly to thwart the habeas corpus petition they had filed in Rhode Island the day before, seeking his release for medical treatment.

    The federal judge who heard that petition on July 31 did not make a ruling, but in an unusual move insisted that Mr. Ng get the care he needed. On Aug. 1, Mr. Ng was taken to a hospital, where doctors found he had terminal cancer and a fractured spine. He died five days later.

    The accounts of Mr. Ng's treatment echo other cases that have prompted legislation, now before the House Judiciary Committee, to set mandatory standards for care in immigration detention.

    In March, the federal government admitted medical negligence in the death of Francisco Castaneda, 36, a Salvadoran whose cancer went undiagnosed in a California detention center as he was repeatedly denied a biopsy on a painful penile lesion. In May, The New York Times chronicled the death of Boubacar Bah, 52, a Guinean tailor who suffered a skull fracture and brain hemorrhages in the Elizabeth Detention Center in New Jersey; records show he was left in an isolation cell without treatment for more than 13 hours.

    When Mr. Ng died last week, he had spent half his life in the United States, his sister, Wendy Zhao, said in a tearful interview.

    Born in China, he entered the United States legally on a tourist visa. Mr. Ng stayed on after it expired and applied for political asylum. He was granted a work permit while his application was pending, and though asylum was eventually denied, immigration authorities did not seek his deportation for many years.

    Meanwhile, his sister said, Mr. Ng (pronounced Eng), who was known as Jason, graduated from high school in Long Island City, Queens, worked his way through community technical college, passed Microsoft training courses and won a contract to provide computer services to a company with offices in the Empire State Building.

    In 2001, a notice ordering him to appear in immigration court was mistakenly sent to a nonexistent address, records show. When Mr. Ng did not show up at the hearing, the judge ordered him deported. By then, however, he was getting married, and on a separate track, his wife petitioned Citizenship and Immigration Services for a green card for him - a process that took more than five years. Heeding bad legal advice, the couple showed up for his green card interview on July 19, 2007, only to find enforcement agents waiting to arrest Mr. Ng on the old deportation order.

    Over the next year, while his family struggled to pay for new lawyers to wage a complicated and expensive legal battle, Mr. Ng was held in jails under contract to the federal immigration authorities: Wyatt; the House of Correction in Greenfield, Mass.; and the Franklin County Jail in St. Albans, Vt.

    Mr. Ng seemed healthy until April, his sister said, when he began to complain of severe back pain and skin so itchy he could not sleep. He was then in the Vermont jail, a 20-bed detention center with no medical staff run by the county sheriff's office. Seeking care, he asked to be transferred back to Wyatt, a 700-bed center with its own medical staff, owned and operated by a municipal corporation.

    In a letter to his sister, Mr. Ng recounted arriving there on July 3, spending the first three days in pain in a dark isolation cell. Later he was assigned an upper bunk and required to climb up and down at least three times a day for head counts, causing terrible pain. His brother-in-law B. Zhao appealed for help in e-mail messages to the warden, Wayne Salisbury, on July 11 and 16.

    "I was really heartbroken when I first saw him," Mr. Zhao wrote Mr. Salisbury after a visit. "After almost two weeks of suffering with unbearable back pain and unable to get any sleep, he was so weak and looked horrible."

    The nursing director replied that Mr. Ng had been granted a bottom bunk and was receiving painkillers and muscle relaxants prescribed by a detention center doctor.

    But his condition continued to deteriorate. Once a robust man who stood nearly six feet and weighed 200 pounds, his relatives said, Mr. Ng looked like a shrunken and jaundiced 80-year-old.

    "He said, 'I told the nursing department, I'm in pain, but they don't believe me,'" his sister recalled. "'They tell me, stop faking.'"

    Soon, according to court papers, he had to rely on other detainees to help him reach the toilet, bring him food and call his family; he no longer received painkillers, because he could not stand in line to collect them. On July 26, Andy Wong, a lawyer associated with Mr. Cox, came to see the detainee, but had to leave without talking to him, he said, because Mr. Ng was too weak to walk to the visiting area, and a wheelchair was denied.

    On July 30, according to an affidavit by Mr. Wong, he was contacted by Larry Smith, a deportation officer in Hartford, who told him on a speakerphone, with Mr. Ng present, that he wanted to resolve the case, either by deporting Mr. Ng, or "releasing him to the streets." Officer Smith said that no exam by an outside doctor would be allowed, and that Mr. Ng would not be given a wheelchair.

    Mr. Ng told his lawyer he was ready to give up, the affidavit said, "because he could no longer withstand the suffering inside the facility," but Officer Smith insisted that Mr. Ng would first have to withdraw all his appeals.

    The account of his treatment clearly disturbed the federal judge, William E. Smith of United States District Court in Providence, who instructed the government's lawyer the next day to have the warden get Mr. Ng to the hospital for an M.R.I.

    The results were grim: cancer in his liver, lungs and bones, and a fractured spine. "'I don't have much time to live,'" his sister said he told her in a call from Rhode Island Hospital in Providence.

    She said the doctor warned that if the family came to visit, immigration authorities might transfer her brother. Three days passed before the warden approved a family visit, she said, after demanding their Social Security numbers. Late in the afternoon of Aug. 5, as Mr. Ng lay on a gurney, hours away from death and still under guard, she and his wife held up his sons, 3 and 1.

    "Brother, don't worry, don't be afraid," Ms. Zhao said, repeating her last words to him. "They are not going to send you back to the facility again. Brother, you are free now."