Curtis Howard stalked 24-year-old Catherine Ayling for two years before stabbing her 10 times and slitting her throat at Crewe and Alsager College in Cheshire where she was studying humanities.
He left her body in the boot of his hire car at Gatwick airport before flying back to the United States.
At the Old Bailey yesterday, Mr Justice Hidden described Howard as 'a cunning, devious, violent and dangerous man'. He added: 'Even after the death of Catherine, it is necessary to protect the public and particularly her sister and her sister's husband - Sylvia and Denis Hartington - from serious harm from you.'
Mrs Hartington shouted 'burn in hell, you bastard' as Howard was led to the cells.
Howard had admitted killing Miss Ayling on his appearance at Lewes Crown Court in July. The prosecution accepted his plea of not guilty to murder but guilty to manslaughter on the grounds of diminished responsibility after psychiatric reports showed he was suffering from mental illness.
The judge said although a life sentence for manslaughter was exceptional, he was satisfied Howard presented a continuing threat.
Lewes Crown Court had been told that Miss Ayling, from Arundel, West Sussex, met Howard five years ago when she was in Boston on a student exchange trip.
He was attracted to her from the outset, phoned her several times a week and pestered her for dates. They went out once.
Miss Ayling returned home when her father died and Howard bombarded her with letters, telephone calls, money and gifts even though she said she did not want to see him again. Despite being barred from the country, he entered Britain in May 1991 using a friend's passport and attacked Miss Ayling at her college.