So why did it take so long to get to court?

Three people have been sentenced for enslaving a woman between 2003 and 2006. The catalogue of their crimes is extreme including rape as well as physical violence, they all amazingly enough appear to be of the religion of peace hate judging by the names.
BBC.

Three people have been found guilty of abusing an Indian woman who was treated like a servant and sexually abused.
The mother of four, 39, from Hyderabad, was employed in three London households as a nanny and domestic worker.
Enkarta Balapovi, 54, was convicted of five counts of rape.
Shamina Yousuf, 33, and Shashi Obhrai, 54, were both found guilty of assault occasioning actual bodily harm. Obhrai, of Northwood, was also convicted of making a threat to kill.
The jury at Croydon Crown Court cleared Aleemuddin Mohammed, 35, of Sefton Avenue, Harrow, of sexual assault.
Obhrai, an optician from Moor Park in Northwood, Balapovi, a butcher, of Charlburt Street in St John's Wood, Mohammed and Shanaz Begum, a shop worker from St John's Wood, were found not guilty of trafficking offences on the direction of the judge.
On one occasion she managed to escape and reach a help centre but Obhrai found her. Jurors heard she held a kitchen knife to the victim's neck and threatened to kill her.

Ok, the people have been found guilty, however I do wonder why it took so long for this case to reach the courts, surely when the woman was abducted back from the shelter at knife point some alarm bells should have been ringing? It might just be that I'm parsing that paragraph wrong though and the knife threat happened later.
Still surely it should not have taken so long for someone to realise that something was terribly wrong here? Particularly the refuge? Granted I'm sure she could have been kept captive in a house, but escape should have been possible or at least a cry for help of some kind. Perhaps indeed she did and the police were too 'politically correct' to take it further if they thought it was 'cultural' it has been known after all.
Granted I don't know all the facts here other than what I've read in the press. But it does seem to be a very long period to actually reach the stage of justice being done (for a given value of justice)
Perhaps someone out there would care to enlighten us further?