There's nothing in the files to suggest who 'Crecheman' was, so I think it's unlikely that he was 'found' by a journalist. I think this story is a leak to the Sun, which seems to be the source copied by other newspapers. Why it should be leaked is the question.
Paulo Reis named him in a blog in 2009.
The files contain a mass uncollated information information. There is nothing in them marked with a huge red arrow indicating "I am Tannerman". But his name is in the files.
Reis did the research.
Reis found his name in the files.
Reis did not make the connection because he was intent on "researching" a different theory at the time.
The initial investigation put his name into the file.
The initial investigation did not connect him to anything because they were intent on working on a different theory at the time.
His name however remained in the file and required no one to leak it from another source ... all they had to do was a little research as Reis did in 2009 and the PJ did not in 2007 ... but this time round researching his connection to the creche and his connection to apartment block 4.