The difficult questions about MI6 and rendition
The announcement that no-one will be charged with involvement in rendition will certainly be a relief to MI6.
But the Libyan case still raises difficult questions.
A four-year long investigation by the police was sparked by the discovery in 2011 of documents in Libya that appeared to come from MI6.
They appeared to show British intelligence had facilitated the rendition - sending a person from one country to another for imprisonment and interrogation - of two men to Libya, where they say they were tortured.
The Crown Prosecution Service issued an unusually long statement on Thursday explaining why they did not believe the evidence supported any charges.
(Pointedly, the police released their own statement saying they had collected 28,000 pages of evidence and that the decision was entirely one by the CPS.)
The CPS statement made clear for the first time that MI6 (without naming the agency directly) had been involved - and included details which throw new light on the transfer of two opponents of Colonel Gaddafi to Libya at a time when Britain was seeking to improve relations with his regime.
The two key areas relate to the issue of authorisation and oversight.
One of the biggest questions surrounding what happened in Libya related to who authorised the operation.
We are always told that sensitive intelligence operations are supposed to be authorised by politicians.
Jack Straw was foreign secretary at the time and, so, many had assumed he must have known.
But the statement from the CPS suggests the real story may be much more complex.
A key line reads that an MI6 officer "sought political authority for some of his actions albeit not within a formal written process nor in detail which covered all his communications and conduct". This sentence bears some examination.
For a start, it says the "suspect" (as the CPS describes him) sought political authority, but does not say they actually received it.
Secondly, it makes the point that the authority was only for some of their actions and not all of them - in other words they did not provide a detailed read-out of what was involved in the operation to the government official.
Finally, this did not take place within a formal written process.
No paper trail
In other words, there was not the type of written warrant - or paper trail - that you would normally expect.
One source has suggested that it may simply have involved a phone conversation with a Foreign Office official (not even a minister).
All of this alleviates some of the questions for Jack Straw but does raise the question about how MI6 was operating at the time and whether it was under the type of political control that would normally be expected for an intelligence agency.
A second question relates to oversight after the events.
In 2007 the Intelligence and Security Committee (ISC) investigated rendition.
In a 75-page report, Libya is not mentioned once. The reason, it seems, is that the committee knew nothing about the case.
In fact, no one did until 2011 when Colonel Gaddafi's regime fell and a series of documents from MI6 were discovered.
Had it not been for regime change, the secret of this operation would have been kept and there would have been no oversight of it.
The criticism of the ISC in the past was always that it knew only about things the agencies wanted to reveal.
There was some suggestion at the time that the failure to reveal the Libya case had been due to poor record keeping.
That goes back to the issue of no formal authorisation having ever been signed.
But it does not explain why no one had thought to bring up the case to the ISC.
Perhaps because few had known about it?
But a recent article suggested that it had been sufficiently well-known that when the head of MI5 learned about it, she had written to the prime minister and there had been a major rift between MI5 and MI6 over the latter organisation's activities.
There has been no official reaction from MI6 or the Foreign Office but they will, no doubt, stress that these events took place 12 years ago in the chaotic early years of the "war on terror" and that systems and procedures have changed.
The "consolidated guidance" on how to treat detainees has now been published.
The ISC has been given more powers to demand documents.
And, after review, the CPS has decided that the evidence does not support a prosecution.
But a question remains - what other secrets from this period remain hidden?