Perhaps Tintin and Haddock told the police certain things, but had to explain about their oath of silence, so they couldn't tell the full story, and the police would respect that.

I'm surprised that anyone really considers Tintin's travelling to be journalism at all.
He seems more of a detective to me, a detective with a strong moral sense of doing good.
After all in which adventures that Tintin embarks upon are the direct result of a journalistic project? Indeed some are simply the result of kidnappings of a friend (Calculus) and are therefore personal affairs where Tintin takes matters in hand for himself. Also Tintin never seems politically motivated, politics happens around him and Tintin remains passive in opinion, the purpose is to solve the crime or mystery.
Other times they are the result of chance such as bumping into people (Flight 714, Red Sea Sharks, Cigars of the Pharaoh).

regards,
mat

There is a reference in Flight 714, page 43, where Tintin compares the strange light in the underground, Sondonesian temple with the tempel of the sun.