Darren Smith, 33, admitted raping a 16-year-old girl in December 1987 and indecently assaulting a 15-year- old on Valentine's Day the following year. Both attacks took place in the Marsh Farm area of Luton, Beds, near Smith's home.

 At the time of the offences only two laboratories in the country were authorised to carry out DNA tests "and the pressure on them was great", said Brian Escott-Cox, QC, prosecuting at the Old Bailey yesterday. He said that as a result "not a great deal" was done to test stains on the girls' clothes until Smith was convicted of murdering the au pair Suschita Jungblut, 20, in 1995.

 It was then that a police officer realised the crimes might be linked and re-opened the investigation, the court was told. Miss Jungblut had only been in this country for a month when she met Smith on a night out at a disco in Dunstable, Beds. He lured her to a playing field where she was sexually assaulted and strangled.

 At the time, Smith was on home leave from a six-year sentence imposed for indecently assaulting and beating a woman who rejected his advances. This attack was in 1991 when Smith was on the run from an open prison where he was serving a sentence for burglary.

 When he jailed Smith for life for Miss Jungblut's "brutal murder" Mr Justice Alliott said when he was eligible for parole "there must be the greatest anxiety that a man as dangerous as you is released".

 Yesterday, Mr Recorder Nicholas Purnell, QC, recommended that Smith should serve at least 15 years "for the protection of the public and to reflect the gravity of the offences".