Detective Chief Inspector Des Thomas, leading the inquiry, believes there are several attackers, each acting independently.
He said: 'We have learnt from our extensive interviewing and 26 arrests that there are a number of exceedingly strange people in our society. Each is a loner, and his bizarre behaviour would appear to be sexually motivated.'
A stud owner spoke for many when he said: 'It was bad enough to know we were looking for a person so degraded and so bestial to be capable of these crimes, but to hear now that there are a number of them defies belief.'
Operation Mountbatten, based at Alton and codenamed after a mare found dead in her stable, was set up with a control room ringed with computers to sift information from well over 1,000 telephone callers. The 26 arrests have not resulted in a charge, although two files are pending.
One is being studied by the Crown Prosecution Service and a second awaits further forensic evidence following the mutilation of an in-foal mare near Lymington a month ago, which led to the mare having to be put down. Her foal also died.
Det Ch Insp Thomas admitted to frustration at the lack of evidence: 'We cannot prosecute a person on information received that he has committed such acts in the past. We need something relevant to the case in hand. We are in a difficulty where there is no confession. Almost all the attacks have taken place unwitnessed and at night.'
Although Operation Mountbatten has been somewhat scaled down since a reduction in the number of cases occurring, four full-time officers remain to investigate all attacks.