Updated

A Frenchman convicted of one of history's biggest trading frauds has returned home to serve prison time after a pilgrimage to the pope and a plea for presidential clemency.

Jerome Kerviel, in footage shown on French television, crossed the border from Italy to France by foot late Sunday night. A police official in the French border town of Menton said Kerviel was in custody just after a midnight deadline to begin serving his sentence.

Kerviel was sentenced to three years in prison in a 2010 verdict that was upheld recently by France's highest court.

Kerviel cost his bank Societe Generale 4.9 billion euros in losses in 2008. He says the bank quietly welcomed his unauthorized trades when they earned money but later turned against him.