LUCASVILLE, Ohio — A condemned man appeared to gasp several times and took an unusually long time to die — more than 20 minutes — in an execution carried out Thursday with a combination of drugs never before tried in the U.S.

Dennis McGuire’s attorney Allen Bohnert called the convicted killer’s death “a failed, agonizing experiment” and added: “The people of the state of Ohio should be appalled at what was done here today in their names.”

An attorney for McGuire’s family said it plans to sue the state over what happened.

McGuire’s lawyers had attempted last week to block his execution, arguing that the untried method could lead to a medical phenomenon known as “air hunger” and could cause him to suffer “agony and terror” while struggling to catch his breath.

McGuire, 53, made loud snorting noises during one of the longest executions since Ohio resumed capital punishment in 1999. Nearly 25 minutes passed between the time the lethal drugs began flowing and McGuire was pronounced dead at 10:53 a.m.