John Lichfield: Sarkozy is likely to exploit this opportunity to the fullest

French presidential candidates exchanged insults on the apparent jihadist explanation of the Toulouse killings as the hiatus on campaigning came to an abrupt end with the news the suspect had been pinned down.

President Nicolas Sarkozy and his principal challenger, the Socialist candidate, François Hollande, had stood apart from the vituperation but the allege- dly al-Qa'ida-inspired murders could have a strong influence on the remainder of the race.

Mr Sarkozy's centre-right party has now accused his principal challenger of trying to use the killings for cynical, electoral purposes. Mr Hollande's campaign retorted angrily, and with more accuracy, that he had done nothing of the kind and accused the Sarkozy camp of a "disgraceful lapse".

It is the President that has been accused of playing the race card by campaigning for tighter controls on immigration and the labelling of halal meat. The fact the presumed murderer, Mohamed Merah, is of Algerian origin with jihadist connections could, therefore, play in his favour.

Commentators suggest the Islamist connections of the suspect would be a "relief" – and possibly an electoral boost – for Mr Sarkozy. They pointed out that, in poll after poll, the only issues on which Mr Sarkozy consistently outscores Mr Hollande are crime, security and terrorism.

Running counter to that theory is the idea that the French authorities knew about Merah's activities long before his suspected murderous spree. For all his rhetoric on the dangers of an increasingly multicultural France, Mr Sarkozy will have trouble explaining how a suspected fundamentalist was, it seems, able to kill seven people before the French intelligence caught up with him.

Such issues have been largely absent from the campaign until now but are likely to be exploited – either prudently or shamelessly – by Mr Sarkozy's camp before voting on 22 April.