There are times when I could cheerfully throttle you!
Now, this is not one that I have come across before, so let's look at the evidence that we have.
This was published in the Netherlands as
The Vanished Corpse.
The artist was signing the frames every third or fourth panel which normally indicates the start or the end of the episode for that day's newspaper.
The story has the copyright of Ibergraf on it which indicates that it was created by a Spanish company.
On balance, I would guess that this was first published as a serial in a Spanish paper and the company then tried to make a little more money by selling a reprint license to different companies such as Nooitgedacht.
If it was reprinted in the UK as a Picture Library, I would put money on Pearson's, World Distributors, Micron or Fleetway. The problem is that it would have been in a spy one such as S.A.T.A.N or Top Secret and I don't know of any that were going in the early 1960s when this was first published. Although it would not be much of a stretch to think that it could have been reused in the late 1960s.
I doubt that it would have been published in a UK paper as it would have only run for a maximum of seven weeks assuming three panels a day, but I have been wrong before so I am happy to be proven so again. Now here is a thought, could it have been printed as a filler story in the Lion or Tiger or equivalent annuals?
Even if I have added nothing to your thoughts, hopefully I have helped someone spark a dim and distant memory.