WASHINGTON (AP) — Treasury Secretary Timothy Geithner says regulators waited four years to penalize Barclays bank for trying to manipulate a key global because the investigation was complex.

Geithner told the Senate Banking Committee he alerted U.S. and British regulators in 2008 when he learned of problems with the London interbank offered rate, or LIBOR. He was then president of the Federal Reserve Bank of New York

Britain's Barclays bank admitted last month that it had submitted false information to keep the rate low. Barclays was fined $453 million. Other banks are being investigated.

Sen. David Vitter, R-La., asked why, four years later, the government hasn't determined which big banks manipulated the LIBOR.

Geithner said such investigations are complex and take a long time.