David Jessel lustgartens in Trial and Error (C 4) and so does Michael Buerk on 999 (BBC 1, Tuesday). Perhaps there's a BBC training course dedicated to the baleful skills of lustgartening, with special workshops like Riding the Break: how to hang off a cliff without falling and Vocal Skills, a practical session aimed at perfecting that characteristic delivery, the spoken equivalent of a thundercloud - low, dark and heavy with its contents.
Certainly there are some basic structures any practitioner should bear in mind. You should, for example, alternate forensic statements of fact ('It was an evening in early spring, 1985. All over Britain . . .') with melodramatic contradictions ('But unknown to the family and to the other villagers of Bestwood near Nottingham the final act of a genuine tragedy was unfolding in the deepening shadows just outside').
Indeed, 'but' is an indispensable word for such programmes, the pivot on which the narrative swings from the official version to a proposed alternative. It occurred again and again in Jessel's investigation of the case of Mark Cleary (convicted of the murder of a 10-year-old boy), marking the pendulum beat of a classic detective-story, between surface appearance and a slowly unveiled hypothesis. Here it was a persuasive one (so persuasive that the film-makers had felt able to omit the customary perhapses and possiblys): that Paul Atherton (also convicted of the murder) had deliberately implicated an innocent man to lessen his own guilt.
The evidence, tellingly, came not from new witnesses or new research but through careful examination of existing statements by witnesses. Some policemen resent this invasion of their professional duties, but they seem to have been guilty of a breach of demarcation themselves in this case. As one expert witness put it, if you had proceeded as the police did in writing up Michael Cleary's first confession (immediately retracted), 'You would be acting as an amateur dramatist, recreating the conversation, not recording it'. If they want to write screenplays, can they blame film-makers for turning detective?