Dirk Greineder got to tell jurors Tuesday that he didn't kill his wife, but he may have suffered for the opportunity. After completing an emotional direct examination, the doctor was put through a blistering cross-examination by the prosecution. He was left, at times, with no response but to shake his head in silence.

"I couldn't imagine living without her, she was truly the best person I had ever known," a tearful Greineder said, referring to his wife, Mabel Greineder, who was murdered while the two were walking their dog near their home. "Life with May was so much more than a sex life. It was all about sharing, about caring, it was about doing little things like the crossword puzzle . . . Most importantly, it was all about family, raising the kids."

His three grown children, who have sat behind their father throughout the three-week trial, sobbed off and on during Greineder's testimony.

Greineder, who is charged with first-degree murder, says he briefly separated from his wife during a morning walk on October 31, 1999, when she was bludgeoned and stabbed to death. His lawyers say the police failed to consider the possibility of a serial killer, noting that two other people had been killed in nearby Massachusetts parks around the time Greineder's wife was slain.

The prosecution, however, claims Greineder needed his wife out of the way to continue his secret life of porn and prostitutes.

He faces life in prison if convicted.

During his second day on the stand, Greineder told jurors about how he graduated from using phone sex lines and Internet pornography sites to paying prostitutes for sex.

Discussing his first encounter, in February 1998, Greineder said, "I felt extremely awkward and uncomfortable about what I was doing and I brought a bottle of champagne thinking that if I did something to make it more sociable it would make it easier for me and for both of us."

But champagne wasn't the only thing Greineder found to alleviate the awkwardness. As his daughter Kirsten sat straight-faced with her arms clasped tightly to her chest — having testified Monday that she'd never heard the full story of her father's sexual exploits — the doctor explained that when "Viagra was released in 1998 ... I felt that it might be helpful."

So helpful was the impotence cure-all that, when Greineder once found himself without the drug on his way to meet Karen Diullio, a prostitute who testified last week about a number of sexual encounters with the doctor, he promptly found an emergency supply.

"I stopped at a local drug store and obtained a second prescription," he told the jury because "that was easier than going home."

Later, this same Viagra created trouble for him at home. His wife found the drug in his travel kit in summer 1998, he testified, and called him to demand an explanation. "I couldn't think of anything other than to say that I had bought them to experiment with," Greineder said.

As he had on Monday, defense attorney Martin Murphy followed up this explicit line of questioning with one that brought out the family man in Greineder, giving his client ample opportunity to show he had no reason to want his wife dead at that time.

Greineder said that complications in settling Mabel's deceased mother's estate led him to revise the couple's insurance policy, and that $50,000 gained in inheritance had already been put toward remodeling the couple's Wellesley, Mass., house.

Greineder told jurors that he stayed up past midnight the night before the murder helping his wife with a school project on asthma by typing the bibliography for her.

Moving on to the next morning, Murphy asked, "When you were making breakfast with your wife that morning, were you planning to kill her?"

"No, I was not," replied Greineder, calmly.

But the defendant seemed less confident when he began to explain how, in the garage, both he and his wife got nosebleeds, a crucial piece of his defense which explains the presence of both of their blood on a white towel Greineder kept in his car. His wife got a nosebleed first, he said, so he gave her the towel to help stop the bleeding. Then, according to Greineder, their dog Zephyr bumped into his nose as he tried to get the dog into the family van, causing his nose to begin bleeding as well.

Describing their walk in the park later that morning, Greineder told the jury that his wife often had back problems and had hurt herself while they were walking Zephyr. To offer a possible explanation for baggies found in the woods and linked by expert testimony to a box of bags in Greineder's house, he noted that his wife could have brought some to collect berries for their birdfeeder.

Made to stand throughout his day-long testimony, Greineder mostly gazed downward at the podium while speaking, giving his lawyer only brief glances and disregarding the jury altogether.

His most emotional testimony came when Murphy asked him to recount how he found his wife lying in the middle of the forest path.

"I was sure she was going to talk to me, but she didn't," he began. "I think I called her name or I said something ... and she didn't open her eyes. I guess all at the same time I saw the cut on her forehead and I knew something had happened. I was shaking so hard, my hand, I couldn't control it."

He seemed to struggle to continue, with tears running down his face, and his veins etched in relief on his wrinkled forehead.

"I leaned forward and put my head next to her face and tried to feel her respiration ... When I couldn't ... I just couldn't imagine. I mean, it just can't happen," he said, sobbing.

"I tried to pick her up. I figured if I can just get her out of there, get some help," he went on. "All I could think of at the time was scoop and run, scoop and run, which is what we used to say in the emergency room, but I couldn't scoop her out of there."

In wrapping up his direct examination, Murphy again questioned Greineder on the importance of his family.

"How did you feel about your family on October 31, 1999, doctor?" he asked.

"It was the most important thing to me in my life. More than work, more than life, more than fame, more than money," Greineder said through tears.

"Doctor, did you kill your wife?" Murphy asked.

"No, I did not," replied Greineder softly.

During his cross-examination, prosecutor Richard Grundy zeroed in on inconsistencies between Greineder's recent testimony and statements he made earlier in the case.

The aggressive Grundy pointed out that, earlier in the day, Greineder told the jury he didn't realize that foul play was involved in his wife's death until he returned to her body after calling police, but in the 911 call jurors heard earlier in the trial Greineder told the operator, "Somebody attacked her, it's definitely an attack."

Grundy also tangled with the defendant on whether the dog had jumped him or bumped him to produce the nosebleed, and he forced Greineder to admit that one of the alternate screen names he used in online adult chat rooms was not "Rider," as he told the courtroom yesterday, but "Pussy Rider."

He then questioned Greineder about the naked photograph that he sent to a couple he met on an online service, and even showed him the picture to ask him to identify it.

Grundy succeeded in confusing the doctor a number of times with his combative style. At one point a frustrated Greineder told the prosecutor, "I'm trying to be as accurate as I can so I can not have you take me to task for what I said this morning."

During a particularly contentious clash, Grundy asked why Greineder had told a detective the day his wife was killed that she had given him a backrub that morning, but during testimony Tuesday had told the jury that they gave each other backrubs.

"She liked to scratch, I like to rub," replied Greineder. "She would scratch and say that's what you should do to me."

"So were you lying to [the detective] or are you lying to the jury?" asked Grundy.

Greineder said nothing and just shook his head.

"I don't remember for sure now, I don't remember what I told Detective McDermott," he continued later.

Grundy was scheduled to wrap up his cross-examination of Greineder Wednesday.

This trial is being broadcast live by Court TV.