TOLEDO, Ohio — An expert in exorcism and other Roman Catholic rituals testified Monday that the murder of a nun in a chapel 26 years ago was committed by someone with specialized knowledge of the church's rites and symbols.

The witness, a Catholic priest who studies the occult and consults on cases of alleged demonic possession, told jurors at the murder trial of Rev. Gerald Robinson that the ritualistic nature of the slaying suggested a member of the clergy was the culprit.

"Certainly a priest would have had that kind of knowledge, possibly a seminarian," the Rev. Jeffrey Grob, associate canonical vicar for the Archdiocese of Chicago, said.

He testified that the circumstances of the killing, including the use of an altar cloth and an apparent anointing of the victim in blood, indicated a more thorough understanding of the faith than lay Catholics possess.

Robinson, 68, is facing a possible life sentence for the murder of Sr. Margaret Ann Pahl. The 71-year-old was strangled and stabbed to death in the sacristy of the Mercy Hospital chapel on April 5, 1980, the day before Easter. Robinson was one of two hospital chaplains. Sr. Margaret Ann's undergarments were pulled down around her ankles and her dress pushed up, exposing her genitals. She had been stabbed 31 times, including nine wounds made through the cloth in the shape of an inverted cross.

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Asked by prosecutor J. Christopher Anderson to identify ritualistic aspects in the crime, Grob sighed and said, "Where does one begin?" He said that in the eyes of the church, a nun was a virgin wed to God and that by leaving Sr. Margaret Ann naked, the killer was "defiling the bride of Christ."

He said profaning what was holy and pure was a hallmark of satanic worship.

"You take innocence and you destroy or mock it," he said. The coroner found she was not raped.

He testified that the upside-down cross was used in satanic ceremonies as an "affront to the sacred." He said the use of the cloth showed a desire to "penetrate" the holy with the evil.

He said a bloody semicircle on the victim's forehead might be evidence that the killer performed a perverse version of the sacrament of last rites on Sr. Margaret Ann. The sacrament calls for the head and hands of a dying or gravely ill person to be anointed with oil.

"It's a reversal. Normally what should be a good Catholic person going to meet God, getting anointed, is now all of a sudden a mocking. [She is] anointed with blood, her own blood," he said.

Four of the jurors hearing evidence are Catholic. Much of Grob's testimony seemed designed for those panelists who are not. He explained the importance of the Easter season and described the liturgies of Holy Thursday, Good Friday, Holy Saturday and Easter. Sr. Margaret Ann was killed on Holy Saturday while she decorated the church for Easter services.

The killer posed her body on the floor of the sacristy, a room off the chapel where the Eucharist is kept in the days leading up to the holiday. Grob said that in the eyes of believers, the murder in the presence of the Eucharist meant the killing occurred in the presence of Jesus.

The prosecutor also questioned Grob about church law concerning the sacrament of confession. When he was interrogated shortly after the murder, Robinson told police that the real killer had confessed to him. He later recanted, saying he felt bullied by officers.

Grob said canon law is clear that priests cannot reveal the identity of anyone who confesses to them and are barred from discussing the content of a confession even if they conceal the person's identity. The penalty for revealing a person's identity is excommunication, Grob said.

"Is this part of the training of all priests?" Anderson asked.

"Yes," Grob replied.

The Rev. Gerald Robinson (left) listens to testimony with his defense attorney John Thebes.

On cross-examination, defense attorney John Thebes suggested Robinson was reacting to stress when he said he had heard the killer's confession. The attorney, a practicing Catholic who has known the defendant since second grade when the priest taught at his parochial school, reminded the witness of the Gospel account of St. Peter, who three times insisted that he did not know Jesus.

"Under stress, St. Peter denies Christ," he asked.

"Well done," Grob said.

"And Peter became the pope of our church," Thebes asked.

"That's what we believe," Grob nodded.

Jurors appeared riveted by the priest's testimony, especially as he described his responsibilities in Chicago. Grob, who is completing a doctoral dissertation on the history of modern exorcisms, said he takes calls from people who believe they are possessed and then assists at exorcisms. Asked how many exorcists work in his archdiocese, Grob said about a dozen.

"There is a need for many more, but that is another discussion," he added.

Also Monday, jurors viewed a videotaped interview a police detective conducted with Robinson shortly after his arrest in 2004. In the hour and 20 minute interview, Robinson said he was innocent, but could not account for the evidence that led detectives to suspect his involvement.

Told by investigator Thomas Ross of the Lucas County prosecutor's office that his letter opener has been forensically linked to blood stains on the altar cloth, the priest replied, "I never paid attention to it because I never used it."

The priest, dressed in a checked shirt in the video rather than the Roman collar he wears to court, remained impassive as Ross informed him that a police lab found a tiny speck of blood on the dagger-like opener.

"Why are you smirking at me? This is serious," the detective thundered at Robinson.

"I'm not smirking," the priest replied quietly. "I was not there."

Robinson also told Ross he had been a suspect over the years because he had an unusually calm disposition.

"They told me I didn't respond normally like a person accused of murder would respond, but I just don't have that in me to holler and scream and demand my rights," he said.

In the interview, Robinson also said that he did not have a key to the chapel sacristy. Two nuns at the hospital previously testified that both chaplains had keys and later in the day, the lead police investigator in the case told jurors he found the statement nonsensical from his personal experience as a youth as an altar boy.

"It's called the priest's sacristy. They go in there to change clothes," Sgt. Steve Forester said.

He said that when he confronted the priest with what he considered a lie, Robinson insisted he was telling the truth.

Because of scheduling problems with prosecution witnesses, Judge Thomas Osowik cancelled testimony Tuesday. The trial is to resume Wednesday morning and prosecutors are expected to rest their case later in the week.