Brian Michael Rini, now 25, said he was sorry during the video hearing before U.S. District Judge Michael Barrett made his sentence official.
"I wish that I could just take it back," Rini said. "I am sorry to the family."
WATCH: Timeline of Timmothy Pitzen case
Kyle Healey, an assistant U.S. attorney, admonished Rini for causing "unnecessary pain" by raising false hope for relatives of Timmothy Pitzen, an Aurora, Illinois, boy who disappeared at age 6 in 2011.
"He needs to understand that when he tells lies like this, it does cause damage," Healey said. "It hurts people, it hurts their families, and it takes law enforcement away from their very serious job of helping children who have been sex trafficked."
Rini, who will get credit for time served, had shown up in northern Kentucky in early April 2019 claiming to be Pitzen. He told authorities he had just escaped captors who sexually and physically abused him for years.
New image released of Timmothy Pitzen, missing Aurora boy
Confronted with DNA results proving he wasn't Pitzen, Rini said he had watched a story about the missing boy on ABC's "20/20" and wanted to get away from his own family, the FBI said.
Rini's DNA was already on file because of his criminal record. He served time for burglary and vandalism.
Barrett told Rini earlier this year he faced a mandatory two-year sentence, but the judge wanted to see results of a presentencing investigation before entering his sentence. Rini will be released on probation in less than four months.
The judge said Rini should receive mental health treatment and counseling, have no contact with the missing boy's family, and can't have drugs or guns.
Rini earlier pleaded guilty to aggravated identity theft. Prosecutors dismissed two other charges.
He twice portrayed himself in Ohio as a juvenile victim of sex trafficking, and in each case was identified after being fingerprinted, authorities have said.
RAW VIDEO: Timmothy Pitzen last seen on surveillance video
On May 11, 2011, surveillance video captured Timmothy's mother, 43-year-old Amy Fry Pitzen, picking him up from Greenman Elementary School in Aurora. She told the school there was a family emergency.
Police said Pitzen took her son to Brookfield Zoo and to Key Lime Cove in Gurnee. On May 12, they checked into the Kalahari Resort in the Wisconsin Dells.
Timmothy and his mom were last seen together on the morning of May 13, checking out of the resort.
Police said Pitzen then checked herself into a motel in Rockford, Illinois, that night. She appeared to be alone.
She was found dead on May 14. She had taken her own life.
Police said Pitzen left a suicide note that said, "Tim is somewhere safe with people who love him and will care for him. You will never find him."
In August 2011, police disclosed they found a "concerning" amount of blood in the back seat of Pitzen's SUV after her death. Tests showed the blood was Timmothy's. Authorities also released a video clip of 6-year-old Timmothy playing a make-believe guitar, hoping that the boy's disappearance would remain in the public eye.
In 2013, Pitzen's cellphone was recovered from a roadside ditch near Rockford. Police said there was no useful information on the phone.
In 2015, the National Center of Missing and Exploited Children released an age progression of what Timmothy would look like at 10 years old. A woman in Rockton, Illinois, thought she saw a boy resembling the image, but it wasn't him.
ABC7 Chicago contributed to this article.
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