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A Detroit-area cancer doctor accused of putting people through unnecessary treatments and then billing insurers for millions of dollars pleaded guilty to fraud Tuesday, admitting that he knew his patients often didn't need chemotherapy.

Dr. Farid Fata pleaded guilty to 16 charges, including money laundering and conspiracy, without the benefit of a plea deal with prosecutors. U.S. Attorney Barbara McQuade said she would not negotiate such a "shocking" case and will seek a sentence of life in prison.

"We weren't interested in bargaining anything away," McQuade said.

"His conduct was so egregious," she told The Associated Press on the courthouse steps. "It wasn't a matter of stealing money but torturing patients by lying to them about having cancer. ... Chemotherapy is poison intended to kill cancer cells."

Fata, 49, of Oakland Township pleaded guilty a month before trial in Detroit federal court. The hearing Tuesday was supposed to be an opportunity to argue about evidence, including an email that showed his interest in a $3 million castle in Lebanon, his native country, at the peak of the scheme.

U.S. District Judge Paul Borman went over the charges and asked Fata each time, "You're pleading guilty freely and voluntarily?"

"Yes," he replied, dressed in jail clothes.

Defense attorney Christopher Andreoff didn't explain Fata's decision and later declined to comment when reached by phone. He told the judge that he and Fata had met more than 50 times to discuss the evidence.

Patients and relatives of former patients were stunned when charges were filed 13 months ago. They protested against Fata on the courthouse sidewalk and still regularly meet to swap stories.

His cancer clinic, Michigan Hematology Oncology, had seven offices and a related business that performed tests to look for cancer. The government says Fata submitted about $225 million in claims to Medicare over six years, about half for chemotherapy and other cancer treatments.  Medicare paid more than $91 million, and private insurers were billed, too.

Jeff Berz, of Utica, said his father, Milton Berz, died in 2008, a year after being diagnosed with leukemia. He recalled the 81-year-old getting treatments while sitting in Fata's parking garage.

"Dr. Fata told my dad it would make it easier. His kidneys eventually failed," Berz said. "Did the drugs kill him or the cancer? I don't have any definitive answers, but I do have my suspicions. Every time I turn around, I'm running into somebody who knows somebody who was treated by Dr. Fata. This is so widespread."

Fata will be sentenced on Feb. 23. Any trial on the remaining charges won't be held until next year.