Jozef Puska has been sentenced to life in prison for the murder of Ashling Murphy in Tullamore on 12 January 2022.
Mr Justice Tony Hunt delivered the sentence, which he described as "wholly deserved", following impact victim statements from the Murphy family, and Ashling's partner, Ryan Casey.
He said he does not have the power to impose a minimum period to be served and if he had the power, a whole life-term would have to be considered in this case.
The judge said Puska's evidence had been "indescribable" and "the one thing we don't know about this case is the why."
He told Puska that "unless that becomes known, the question of your safe return to society must be an open one."
Mr Justice Hunt concluded by saying, "very well, you may take him away," before six prison officers led Puska to the cell area.
Puska, 33, of Lynally Grove in Mucklagh, Co Offaly, was found guilty of murdering Ms Murphy, 23, by a jury of nine men and three women last week.
The jury found the father of five, who is originally from Slovakia, guilty of murdering the primary school teacher in a random stabbing as she walked along the Grand Canal last year.
She had been stabbed 11 times.
Puska did not know Ms Murphy, they had never met and there was no connection at all between them.
Puska was placed at the scene by the presence of his distinctive green and black bicycle close to where Ms Murphy was found.
He had been captured on CCTV cycling the same bicycle around Tullamore earlier that afternoon, following two women before heading towards the canal where he isolated Ms Murphy, who was walking alone.
Puska's DNA was found on the bike as was his fingerprint and his DNA was under Ms Murphy's fingernails.
The prosecution argued that the DNA under the nails showed that she had scratched her attacker as she tried to save her own life. When gardaí spoke to Puska the day after the murder his face and hands were covered in scratches that were consistent with him crawling through the thorns and briars by the side of the towpath where he murdered Ms Murphy.
In his testimony to the trial, Puska claimed that he was cycling along the towpath when he was attacked and stabbed by a masked man.
He claimed the same man then attacked and stabbed Ms Murphy before running away.
In what prosecution counsel Anne-Marie Lawlor SC described as a "foul and contemptible fabrication", Puska claimed that he then tried to help Ms Murphy.
The jury rejected his version of events.
No motive has been offered for the killing.
Earlier, the judge presiding over the trial has said he does not accept that the convicted killer did not remember confessing to the murder.
Puska told gardaí who visited him in St James's Hospital that he did it but later claimed he could not remember that.
Mr Justice Hunt said "I don't agree that he had no recollection to offer" and believes Puska was in possession of his full faculties and capable of asking and answering questions.
"I don't accept that he had amnesia of that kind or anything like," the judge said, adding that there is no conspiracy that the gardaí were at the hospital to extract a confession.
He also said there is no evidence that stress or low-level pain or discomfort made it improper for gardaí to engage with Puska in hospital.
Before hearing the statements the judge outlined the legal reasons behind his rulings on pre trial applications to exclude certain evidence from the trial including CCTV and admissions made by Puska while he was in hospital.
The judge said a ruling from the higher courts on privacy rights was long overdue as the courts were having to deal with a "familiar suite of privacy rights arguments" that had been around for the past five years or so.
He said he did not believe Puska's privacy rights were breached in admitting the CCTV of him cycling around Tullamore and believed most reasonable people would trade their privacy rights to have serious crime detected and punished.
The judge is also detailing the reasons behind his decision to allow a confession made by Puska while in hospital and said there was no requirement for a suspect to be medically assessed before speaking to gardaí.
