Raffaele Sollecito is stopped by police close to the Austrian border, after judges reinstated his and Amanda Knox’s murder conviction for the death of British student Meredith Kercher.
The appeal from Italy’s supreme court on Thursday night overturned a previous appeal from 2013 that found the pair not guilty.
Mr Sollecito was sentenced to 25 years and Ms Knox, jailed for 28 years and six months.
Hours before the verdict was announced, Mr Sollecito left the hearing in Florence in central Italy and began travelling north, his lawyer telling reporters he would not attend to hear the verdict due to stress.
Police say they found the 29-year old between the northern towns of Udine and Tarvisio, close to Italy’s border with Austria, which he had reached by Thursday afternoon.
It is not clear whether Ms Knox, 26, will be expected to return to Italy to serve her jail term, but in a pre-recorded interview for BBC’s Newsnight, she said: “I’m not willingly going back, no.
“It would feel like a train wreck. There’s not a lot I can do after this appeal. They would order my arrest and the Italian government would approach the American government and say, ‘Extradite her’.
“And I don’t know what would happen. I’m still counting on an acquittal.
“I’ll technically be considered a fugitive. I don’t know what I will do though. I’m definitely not going back willingfully.
“They’ll have to catch me and pull me back, kicking and screaming into a prison I don’t deserve to be in.”
Speaking after the case, Ms Knox issued a statement in which she was “frightened and saddened” and was going to appeal against the decision.
She described the ruling as “inconsistent and unfounded” and her co-accused was said to have been “astonished” with the way the court kept changing its mind.
Neither defendant was in the courtroom as the verdict was announced, though Mr Sollecito, 29, had attended the lengthy hearings.
Members of 21-year-old Miss Kercher’s family were there to hear the verdict – and said they would not be able to forgive those responsible for her death.
Miss Kercher, a Leeds University exchange student from Coulsdon, Surrey, was found with her throat slashed in the bedroom of the house she shared with Ms Knox in Perugia, central Italy, in November 2007.
The defendants were originally found guilty of murder in 2009, and were handed jail terms totalling more than 50 years.
They were cleared nearly two years later – but the appeal court ordered a fresh trial in March last year.
Rudy Guede, a drug dealer, is serving a 16-year sentence over the death, though the courts have said he did not act alone.