According to Peter Hill the McCann 'side' leaked continuously. I certainly wouldn't trust them to keep things confidential.
The fact of the matter is that there was a news story every day and both sides in this particular case were briefing and leaking all the time, every day; every single day people were being briefed by one side and the other side.
https://publications.parliament.uk/pa/cm200910/cmselect/cmcumeds/362/9042803.htm
According to Peter Hill once Kate and Gerry were made arguidos they were bound by the secrecy laws from defending themselves against the leaks from the Portuguese police ...
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Mr Hill: That is a very, very good question.
In this particular case, as I explained to you, the Portuguese police were unable, because of the legal restrictions in Portugal, to make any official comment on the case.
What happened was that they resorted to leaking things to the Portuguese press.
We did our best to check up on these things but of course it was not very easy to do so.
We always put the stories to Mr and Mrs McCann's PR team but most of the time the people they had then, after the McCann's had been named as suspects, did not return our calls.
So this was a more difficult situation than any of us had ever encountered. Yes, there was a clamour for information and we did our best to provide it. Of course we do check as thoroughly as we can. Newspapers operate at very high speed and it is quite true that sometimes it is not possible to check things as thoroughly as you would like.
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Q619 Chairman: You said in your apology: "We trust that the suspicion that has clouded their lives for many months will soon be lifted". You will acknowledge that the reason for that suspicion was in large part the activities of your newspaper and other newspapers?
Mr Hill: No. We were part of that process but the principal reason for that suspicion has to be laid at the door of the Portuguese police.
They were the people who named Mr and Mrs McCann as the suspects and repeatedly questioned them for many, many hours and they were the people who leaked all the information about them.
Yes, we were reporting what happened. The alternative would have been for the British press not to report anything. Do you think that would have been a possibility, when the rest of the world was reporting on this case, for the British press to say nothing? It is not practical.
We are all talking here in hindsight and hindsight is a marvellous thing but the fact of the matter is that at the time these reports and these leaks were happening on a daily basis and that is the truth.
https://publications.parliament.uk/pa/cm200910/cmselect/cmcumeds/362/9042803.htm