DEDHAM, Mass. (Court TV) — Even before he was charged with using a hammer and knife to brutally murder Mabel "May" Greineder, Dirk Greineder cautioned the dead woman's older sister that she might hear some "bad, ugly things" about him.

Dirk Greineder did not tell Ilse Stark what those things were but the New York woman would soon learn a lot she hadn't known about her brother-in-law, a renowned Boston area allergist.

Greineder, police and prosecutors claim, pursued a lifestyle in secret that centered around Internet pornography and prostitutes — including one he allegedly called to arrange a tryst the day after the Oct. 31, 1999, murder in the Morse's Pond Recreation Area, a wooded park near the Greineder home in Wellesley.

Prosecutor Richard Grundy maintains that Greineder concocted a plan to kill his 58-year-old wife and burn the evidence with lighter fluid, but that the plan went awry. Greineder, who pleaded not guilty, claims someone else killed his wife and police focused on him only because police were already stumped by two unsolved killings in the area.

Testifying Monday for the prosecution, Stark, the victim's sister, told the jury that Greineder appeared to be trying to explain incriminating physical evidence before his Feb. 29, 2000, arrest. Greineder, according to Stark, offered a theory that his DNA might have been transferred by Mabel Greineder to her attacker in one of two ways.

During the weeks Wellesley and Massachusetts state police officers were investigating the killing, Dirk Greineder told Stark that both he and his wife suffered what Stark called "simultaneous nosebleeds" and shared a towel before the murder.

Mabel Greineder suffered from regular nosebleeds but there has been no testimony that Dirk Greineder, 60, shared the medical condition.

Dirk Greineder also told Stark, according to her testimony in Norfolk County Superior Court, that he and Mabel Greineder both threw a ball to one of their two dogs and theorized that there could have been some DNA transfer that way.

"He said they had taken the spongy ball to play with and May had thrown it and he had thrown it," said Stark, a diminutive woman with short auburn hair. "He said, 'If May had defended herself, it is very possible that DNA from the dog and myself could be on the glove.'"

Defense attorney Martin Murphy asked Stark only a few questions during his 14-minute cross-examination of the witness, the first of nine to give testimony Monday. He did not ask Stark any questions about Greineder's theories about why his DNA might be found on incriminating pieces of evidence.

Stark's testimony was followed by yet more damaging physical evidence against Greineder, who has already been linked by DNA to a pair of brown work gloves police found in a storm drain near the crime scene. Fingernail scrapings from Dirk Greineder contained cotton fibers similar to fibers found on the inside of the brown gloves, a Massachusetts state police criminalist testified.

Elizabeth Fisher, a trace evidence analyst, conceded on cross-examination by Murphy that cotton fibers are the most common fibers in the world and that she could not establish scientifically that Greineder wore the gloves believed to belong to his wife's killer.

The jury, eight men and two women, appeared bored by the additional testimony about physical evidence but was attentive, despite the heat in the un-airconditioned courtroom, while Stark was on the stand. Stark, dressed in a black-and-white sleeveless dress and pearls, looked directly at the panel as she testified, offering anecdotes to show that she and Mabel Greineder — who she called "May" — were best friends as well as siblings.

Stark said Dirk Greineder appeared agitated and nervous two days after the killing, when he took his sister-in-law aside and asked her to borrow an unspecified amount of money. The police were suspicious and anxious to make an arrest, Greineder told Stark, according to her testimony.

"He stated that they were bastards and that the reason they were after him was because they didn't go after anyone else, and they had to come up with someone to solve this crime, and that there had been similar crimes in the area," Stark testified.

The testimony played somewhat into the hands of the defense. Murphy is trying to convince the jury that police targeted Greineder early, refused to look for other suspects and failed to consider that Mabel Greineder could have been killed but the same person responsible for two other unsolved killings of elderly people in nearby towns.

When Greineder found out shortly before his arrest that Stark had been talking to Trooper Martin Foley and Wellesley police Det. Jill McDermott, he was not pleased, according to testimony. "He said, 'You think you're their friend ... They're not as nice as you think they are,' " Stark testified.

Greineder's three adult children — Kirsten, Colin and Britt Greineder — sat together on a hard wooden bench as they have throughout the trial. Colin Greineder looked at the floor and clenched his fist as several prosecution witnesses testified that the hammer, knife gloves, lighter fluid and other items found at the crime scene were all available at Wellesley stores where he regularly shopped.

Britt Greineder, dressed in a short blue-and-white sun dress, wept openly as Stark recalled the phone call she received notifying her that her only sister was dead.

"Britt said, 'Aunta Isle, there's been an accident ... My mother is dead," Stark testified. "I said, 'How's your father?' She said, 'No, my mother's dead. Someone hit her on the head.' "

Approached outside the courthouse, Stark turned and walked away when a reporter asked if she believed that Dirk Greineder killed her younger sister.

Testimony resumes at 8:30 a.m. Tuesday. The trial, pre-empted Monday by coverage of the execution of Oklahoma City bomber Timothy McVeigh, is being broadcast by Court TV.