A shortage of one of the three drugs used in most lethal injections has caused disarray as states pursue a desperate and sometimes furtive search that might run afoul of federal drug laws.

At the same time, it has given death-penalty opponents fresh arguments for suing to block executions.

Until recently, states that use the drug, the barbiturate sodium thiopental, got it from a domestic supplier, Hospira Inc. But that company stopped making the drug in 2009 because of manufacturing problems and announced this year that it would stop selling the drug altogether. International pressure on suppliers by groups opposed to the death penalty has further restricted access to the drug. States had to find a new source, but importation of sodium thiopental is highly restricted under federal law.

Recently released documents emerging from lawsuits in many states reveal the intense communication among prison systems to help one another obtain sodium thiopental, and what amounts to a legally questionable swap club among prisons to ensure that each has the drug when it is needed for an execution.