There is a gathering sense here tonight that this investigation is finally gaining momentum. This was a crime, which of course shocked, but quite swiftly seemed to baffle police, as they searched for a motive and then it seemed to frustrate them, as they searched for evidence.
As much as French investigators are trying to play down events here, they say the man being questioned here is being questioned as a witness, not as a suspect but it is really hard to disguise the idea that a breakthrough might be imminent.
The man we know was a former policeman. It has been reported by French media that weapons were found at his home. French police have four days to question him before charging but tomorrow the prosecutor is talking about holding a press conference. That suggests there is something significant to say.
More top news
Leaked documents have revealed the first known picture of Mohammed Emwazi - named as IS militant Jihadi John - as a student in London.
With March just around the corner it's looking like this winter will be the sunniest on record (data goes back to 1929).
A campaign demanding an end to the taxation of sanitary items will be presented to George Osborne after reaching almost 200,000 signatures.