Updated

Spanish police say they have arrested a former JPMorgan Chase & Co. trader wanted by the United States for allegedly falsifying bank records to cover up $6 billion in trading losses.

A statement said Spaniard Javier Martin-Artajo, 49, was arrested Tuesday after he presented himself at a police station in Madrid.

U.S. prosecutors earlier this month filed criminal charges against Martin-Artajo and another ex-JPMorgan trader, Julien Grout.

Martin-Artajo and Grout were accused of marking up the market value of an investment portfolio to hide its plummeting value. The portfolio eventually incurred a $6 billion loss, which was attributed for months to Bruno Iksil, a trader who became known as the "London Whale".

Martin-Artajo was to be brought before the National Court in Madrid as part of extradition proceedings.