Mexico ? U.S. refineries bought millions of dollars worth of oil stolen from Mexican government pipelines and smuggled across the border, the U.S. Justice Department told The Associated Press — illegal operations now led by Mexican drug cartels expanding their reach.

Criminals — mostly drug gangs — tap remote pipelines, sometimes building pipelines of their own, to siphon off hundreds of millions of dollars worth of oil each year, the Mexican oil monopoly said. At least one U.S. oil executive has pleaded guilty to conspiracy in such a deal.

Today, the U.S. Homeland Security department is scheduled to return $2.4 million to Mexico’s tax administration, the first batch of money seized during a binational investigation into smuggled oil that authorities expect to lead to more arrests and seizures.