There is an ongoing scandal in Carmarthenshire, where the question of unlawful payments to the Chief Executive of Carmarthen Council became a national scandal. For the background on this see:

http://www.walesonline.co.uk/news/wales-news/police-launch-investigation-unlawful-payments-6701913

As a result it was decided that there would be a police investigation. However, it was decided that because council and police in the area had many joint undertakings, the investigation would be undertaken by an outside force. Gloucestershire and Avon police were chosen to do this investigation:

http://carmarthenplanning.blogspot.co.uk/2014/02/gloucestershire-police-to-investigate.html

After three months, the police called off the investigation saying there was no case to answer:

http://carmarthenplanning.blogspot.co.uk/2014/05/police-call-off-investigation.html

However, a local blogger was not satisfied with this and asked the police how they had come to this conclusion:

http://carmarthenplanning.blogspot.co.uk/2014/06/unlawful-payments-police-foi-response.html

Here is what she says:

Following the conclusion of the police investigation I made a freedom of Information request to Gloucestershire police. The response came today and there is a link at the end of this post.

I asked for;

1. A list of any persons interviewed, and /or job titles, and whether any of these were 
interviewed under caution 
2. Correspondence between Gloucestershire Constabulary and Carmarthenshire County 
Council
3. Whether or not the Crown Prosecution Service were involved and if so, any relevant correspondence. 

The responses were that;

….nobody was interviewed,
….there was no correspondence between the council and the police and
….the CPS weren’t involved.
This was, you recall, a three month long criminal investigation….

I also asked for;

4. The final report following the conclusion of the investigation 

5. A list, or summary, of all documents in either paper or electronic form which formed part 
of the investigation.

These were refused under the Section 30 exemption in that the release of this information may jeopardise police tactics in the future…presumably they’re expecting a flurry of similar local authority unlawfulness.

A thorough investigation? We’ll have to take their word for it. I remain of the view that in both instances there was, amongst other matters, the deliberate prevention of proper scrutiny as documented in the two Wales Audit Office reports.The full FOI response can be read here.
I am now considering whether to request an internal review of their response.