LUCASVILLE, Ohio — Ohio called off the execution of an ailing 69-year-old killer Wednesday after the executioners couldn’t find a vein to insert the IV that delivers the lethal drugs.

It was only the third time in modern US history that an execution attempt was halted after the process had begun.

Alva Campbell, condemned to die for killing a teenager during a carjacking 20 years ago, will be sent back to death row while authorities consider their next step, including whether to make another attempt to put him to death, Ohio Correction Director Gary Mohr said.

The execution team worked for about 25 minutes to find a vein in Campbell’s arms or his right lower leg as he lay on a gurney in the death chamber. Team members used a device with an ultraviolet light to locate veins while comforting Campbell by patting him on the arm and shoulder.

Although it appeared the executioners had successfully inserted a needle in his shin, the warden instructed the team to pull it out, said David Stebbins, Campbell’s public defender.

Informed the execution was being called off, the condemned man shook hands with two members of the team and wiped away tears.

‘‘This is a day I’ll never forget,’’ Campbell said, according to Stebbins.

Certain conditions can make it difficult to find suitable veins, including damage from drug abuse, or dehydration. Stebbins said Campbell’s poor veins and other health ills are problems that won’t end anytime soon.

Death penalty opponents called for the state to put an end to executions.

‘‘This is not justice, and this is not humane,’’ said Mike Brickner of the Ohio chapter of the American Civil Liberties Union.

Campbell suffers from breathing problems from a longtime smoking habit and needs treatments four times a day, according to his lawyers, who said he also requires a walker and a colostomy bag.

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