A convicted German paedophile got a job as a children's nurse in north London because he had no European criminal record, it has been revealed.
Lars Gellner, 37, arrested at Northwick Park Hospital in Harrow, had been convicted in his absence by a court in Cambodia for attacks on young boys.
Police said that no blame should be attached to the hospital, which "did everything they could to carry out the criminal checks on him and they came back showing nothing."
Gellner was later placed on the sex-offenders register and charged with fraud for not including his criminal record on his job application.
But the case has been thrown out at Aylesbury Crown Court because of a problem with documents sent from Cambodia. It is believed Gellner is being held at a remand centre while his future is decided.
Christine Beddoe, director of End Child Prostitution and Trafficking, said: "This highlights the gaps and weaknesses of international sex-offender management that put children at risk here.
"If the home secretary is serious about getting tough on sex offenders who travel abroad, she should be making all efforts to close loopholes and work more closely with counterparts in Europe and Asia."