Neither the appeals to the Supreme Court, nor his lawyer’s arguments of mental incapacity, nor the Mexican government’s pleas for clemency to Texas Gov. Rick Perry prevented Angel Maturino Resendiz from keeping his date with death on June 27.

When I heard that the execution had finally taken place, I got that same creepy feeling I’d experienced when I sat before the so-called Railroad Killer on death row in October of 2000. It is like being faced with death and not being able to justify it. It is a complex theory: A person takes another’s life and has to pay with his or her own. It doesn’t solve anything, yet justice is being served.

The judicial system has its ways of determining if a murderer was in his right mind when he committed a crime and if, once convicted, he is mentally competent to have the death sentence applied. But what’s clear to me is that when I sat down in that maximum-security prison in Texas to interview Maturino Resendiz, I was not in front of a sane man.

How else could anyone explain why the Mexican drifter felt no remorse when describing not only the murder for which he was convicted, but the other 15 he was suspected of and the ones he attributed to himself?

Resendiz told me he never killed anyone in Mexico, where he was known as a model citizen: a loving son, a caring father and a concerned teacher. Why then, Iasked, did he kill in the United States?

“I began to get angry after the children were killed in Waco (Texas),” he said. “People have forgotten the deaths of those innocent children, but I always have them in my mind.”

What did Dr. Claudia Benton -- whom Resendiz admitted to killing in 1998 -- have to do with the death of children in Waco? “Walking by her house near the railroad tracks, I perceived there was evil inside,” he told me. According to the killer, that led him to enter and find a computer where she had records of experiments with babies.

Why kill the couple in Weimar, Texas? “They had books on black magic, on the occult,” he replied. What about Noemi Dominguez, a 26-year-old teacher? “She had pro-abortion literature,” he claimed.

The list of alleged victims is long. It includes eight in Texas, two in Illinois and Florida, and one each in Kentucky, California and Georgia. But Resendiz told me the authorities were off by a long shot.

He laughed when I asked him if there had been others. “There are many, many more,” he said. So many that he lost track. The majority, he claimed, were homosexuals who could not enter the gates of heaven. But he would never divulge the details. “If I give them all the information, they will not do their job to investigate. Now there will always be that doubt, if it was me or someone else.”

During our interview, Resendiz -- with whom I had exchanged many letters while he was in jail -- sent contradictory messages. He claimed not to regret any of the murders, yet wished they had not happened. However, before dying by lethal injection, he apologized to the families of his victims. He said he allowed the devil to run his life, and he deserved to die.

I’m sure we would all like to understand what goes through the mind of a serial killer, particularly one who picks his victims at random. In the case of the “Railroad Killer,” the only clue to his murderous spree is his philosophy on death.