Documents released Friday afternoon in the case of Arizona’s execution of Joseph Wood show that executioners used 15 separate doses of a new drug cocktail before Wood finally died.

According to witnesses, Joseph Wood gasped for air and struggled repeatedly during the two-hour process. Wood, 55, was sentenced to death twice for the 1989 murders of his estranged girlfriend, Debra Dietz, and her father, Eugene, in Tucson.

Wood’s lawyers say the number of doses is further proof that the execution was botched. Lawyers had warned that the combination of 50 milligrams hydromorphone (a pain killer) and 50 milligrams of midazolam (a sedative) was rife with potential problems.

“Instead of the one dose as required under the protocol, ADC injected 15 separate doses of the drug combination, resulting in the most prolonged execution in recent memory,” said Dale Baich, Wood’s lawyer. “This is why an independent investigation by a non-governmental authority is necessary.”

Ohio used a similar drug cocktail in January to execute Dennis McGuire, who gasped and snorted for 25 minutes before finally dying. It was the longest execution in Ohio history.

When officials in Ohio and elsewhere first expressed their intent to experiment with the midazolam/hydromorphone combination, experts predicted that little was known about how the new drug combinations would work in executions.

State officials are using new drug combinations because pharmaceutical companies are refusing to sell or export the drugs traditionally used in executions. The US has seen a shortage of those drugs for several years now.

Wood’s attorneys previously filed motions for injunctions because the Department of Corrections would not reveal information about where it obtained its supply of midazolam and hydromorphone or about the executioners’ medical qualifications.

The major question in the motion for stay of execution was the drug midazolam, which has been part of three other executions since last October in which the inmates seemed to gasp for air and take longer to die than with other drugs used in lethal injection.

The debate over Wood’s execution has played out in the international media, and has called into question whether lethal injection will remain a viable form of capital punishment.