Updated at 6:54 p.m. ET: Jerry Sandusky's wife, Dottie, took the stand Tuesday as a defense witness in her husband's child sexual abuse trial, saying she never heard or saw her husband of 45 years behaving inappropriately around children.

The Sanduskys took a deep interest in the welfare of children because the couple were unable to have children of their own, she testified on the sixth day of her husband's trial in Bellefonte, Pa., on 51 counts alleging that he abused 10 boys over 15 years.

"We had been trying for a while, and nothing happened," Dottie Sandusky said under questioning from lawyers for her husband.

At first, the couple, who are the parents of six adopted children, took in foster children. But "we knew we couldn't take any more kids into our family, and Jerry felt there was a need to start a home or foundation like that," she said.

Prosecutors depict Sandusky, the former longtime defensive coordinator for the Penn State University football team, as having used his connection to one of the nation's premier college football programs to "groom" the boys, whom he met through his Second Mile charity for troubled children, for sexual relationships.

Although speculation has swirled around the case from the beginning about whether Dottie Sandusky knew of her husband's alleged behavior, she hasn't been charged with a crime. She said Tuesday that she had never seen or heard her husband engaging in anything inappropriate.

Once or twice a month, other parents' children — including some of the men who testified against Jerry Sandusky — would stay overnight with the Sanduskys, she testified, apologizing several times for not being able to remember when.

Some of the alleged victims testified that Jerry Sandusky would almost always take them to the basement. One of them testified that he cried out for help as Sandusky raped him but that no one came to his assistance.

But Dottie Sandusky testified that when children stayed over, they were given a choice of where to sleep: in the basement or on the first or second floors. She said, in contradiction of testimony that the room seemed to be soundproofed, that she was able to hear sound coming from the basement while upstairs and that she never heard anyone calling out for help.

Asked why so many witnesses would want to tell the same lie about her husband, she said, "I don't know."

Psychologist: Mental disorder could explain behavior
Dottie Sandusky testified for about an hour, following a psychologist who told jurors that her husband has a personality disorder that leads him to behave in grandiose ways that observers might consider inappropriate.

Prosecutors presented a string of witnesses — including eight of the alleged victims — who described attentive behavior that progressed to inappropriate advances, oral sex and, in some cases, rape.

But the defense expert, Elliot Atkins, a psychologist in private practice in the Philadelphia area, said "histrionic personality disorder" could explain the alleged grooming behavior, a conclusion he said he reached after interviewing Sandusky for six hours and reading his autobiography, "Touched," and intimately personal email messages Sandusky sent to some of his alleged victims.

Histrionic means "dramatic" or "theatrical." People with the disorder desperately seek the approval of others and behave dramatically or inappropriately to get attention, according to the Cleveland Clinic, one of the nation's leading medical centers.

Atkins provided a similar description, saying people with the disorder "might do something dramatic to draw attention to themselves," including behaving in a way that is "inappropriately sexually provocative."

Does it matter if Sandusky has a personality disorder?

"Someone would likely, under those circumstances, desperately attempt to maintain or re-establish that relationship" with someone who had dropped out of his or her life, as Sandusky appeared to do in his email messages, Atkins said.

As part of his ruling allowing Sandusky to present the psychological evidence, the judge ordered that he also undergo an examination by a prosecution expert. Atkins acknowledged that the prosecution examiner disagreed with his assessment.

Gail Saltz, an associate professor of psychiatry at New York Presbyterian Hospital Weill-Cornell School of Medicine, said the diagnosis was highly controversial in her field.

"This would be an incredible stretch — so much that it disturbs some of my colleagues that they are bringing it up," Saltz said in an interview Tuesday on NBC's TODAY.

"This diagnosis has no bearing on your moral compass, your ability to understand what's legal," she said. "It has nothing to do with being a pedophile. it has nothing to do with sexual behavior toward children."

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A string of character witnesses, meanwhile, described Sandusky him as a good and caring man with a stellar reputation in the community.

Lance Mehl, who played for Sandusky at Penn State before spending eight years in the National Football League, called Sandusky a "class act." Kelli Simco, who attended Second Mile for much of her childhood and wrote a newspaper column defending him last year, told how Sandusky arranged to pay her college tuition. Tennesa Inhoof, another woman who attended Sandusky's camps, called him "a very respected man in the community for Second Mile and all the other things he did for the kids."

Another witness said one of the men who testified against Sandusky, describing multiple incidents of alleged abuse, was unreliable and dishonest.

Megan Rash, an Army veteran who said her late brother was close friends with the man, identified in the indictment as "Victim 4," said he "was a dishonest person and embellished stories."

On cross-examination, Rash acknowledged that she had suffered a brain injury in the service and said she couldn't remember where she was deployed.

Another character witness, Jack Willenbrock, a former Penn State professor, called Sandusky "a father figure" who was "respected for what he did professionally."

On cross-examination, Willenbrock said he refused to believe the allegations against his longtime friend and had told acquaintances never to discuss them in his presence.

Defense: Police coached witnesses
Sandusky's attorneys also strongly suggested that state investigators "tainted" the investigation by telling alleged victims that there were other victims and by "refreshing" their memories after they initially said little about Sandusky in police interviews.

Pennsylvania State Police Cpl. Scott Rossman responded that it wasn't unusual for victims of sexual assaults to be reluctant to tell their stories at first. He said that at no time did investigators ever tell potential witnesses what to say.

But Sandusky's attorneys repeatedly indicated that they believed Rossman and retired state Trooper Joseph Leiter coached witnesses, zeroing in on an audiotape of their interview with alleged victim No 4.

In the tape, Benjamin Andreozzi, the attorney for alleged victim No. 4, was heard giving Leiter suggestions on how to get his client to give specifics of his relationship with Sandusky.

"Can we at some point in time say to him, 'Listen we've interviewed other kids, and other kids have told us there was intercourse and that they've admitted - is there anything else you want to tell us?'" Andreozzi was heard having said.

"Yep, we do that with all the time with other kids," Leiter was heard responding.

Andreozzi, who was called to the stand to verify the authenticity of the recording, said his client was "clearly emotionally distraught by having to go in and speak with the authorities" and that it took some time for the man to open up.

As part of their attempt to prove that the alleged victims were seeking to cash in on the case, Sandusky's lawyers also questioned Andreozzi about a possible civil suit for damages.

After lengthy discussion about what he could say under attorney-client privilege, Andreozzi reluctantly acknowledged that a guilty verdict "could have an impact, yes," if the man filed a lawsuit.

John Q. Kelly, a former New York prosecutor who specializes in high-profile criminal defense cases, said the defense had few other options unless they take the risky decision to put Sandusky on the stand. CBSNews reported Tuesday that Sandusky would testify, but his lead attorney, Joseph Amendola, refused to confirm the report.

"I think they just have to say none of it is factual, didn't happen, never went on," Kelly said in an interview on NBC's TODAY show.

"They have to do that by showing the times, the events, the places were all sort of vague and they couldn't nail down the details," Kelly said. "Therefore you have to ignore it."

Closing arguments are expected Thursday, and the jury could begin deliberations as early as Thursday afternoon.

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