A blood stain expert recreated Mabel Greineder's last tragic moments Thursday, using blood spatter patterns to place a stained pair of shoes, gloves, a backpack, and a windbreaker on the killer who bludgeoned and stabbed her to death October 31, 1999.

The testimony dealt a damaging blow to the defendant, Dirk Greineder, accused of killing his wife of 32 years to pursue a secret life of porn and prostitutes.

The expert, Lieutenant Kenneth Martin, of the Massachusetts state police, began by telling jurors how blood marks on the Boston doctor's shoes, a tattered, white pair of Reebok sneakers, appeared to be caused by an "impact-type spatter," the type of blood marking that could be caused when someone is struck with blunt object. Other stains, such as the blood smears on the arms of Greineder's green and blue windbreaker, are the type caused by coming into contact with a bloodied victim.

Greineder, who is charged with first-degree murder in the killing, maintains his innocence, saying he briefly separated from his wife during a walk on the morning she was bludgeoned and stabbed to death in a park near the couple's Wellesley, Mass. home. 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 at the time Greineder's wife was slain.

The prosecution, however, claims Greineder needed his wife out of the way in order to continue a secret life packed with porn, prostitutes and swinging. On Wednesday, the jury heard testimony from a woman Greineder allegedly met through an escort service.

Earlier in the trial, prosecutors called a DNA expert who said Greineder's DNA matched that found on a bloody glove and a pocket knife left in a storm drain near where his wife was murdered. A two-pound hammer also used to kill Mabel Greineder was found there as well.

After linking Greineder to items found discarded in a sewer drain near the site of the murder, and after attempting to establish motive by detailing his secret, illicit life of sex trysts, prosecutors returned to that forensic evidence Thursday in an apparent attempt to place Greineder at the murder scene.

By analyzing the patterns of blood stains found on a number of pieces of evidence, Martin, a Massachusetts state police expert on blood stains, got prosecutors one step closer.

The bald-headed blood expert, dressed in a demure black suit with a red-checked tie, used a laser pointer and a projector to highlight several small areas of rust-colored flecks on the base of Greineder's Reebok shoes. A confident witness, Martin seemed to lecture the jurors with each question. "We're talking about stains that are very small in nature," he said.

Martin said he looks for the "directionality" of a blood stain — the way that blood lands on a surface — to determine what caused it to leave in the first place. Impact-type spatters are caused by bludgeoning like the type of blows that contributed to the death of Mabel Greineder.

The state police lieutenant described staying up "into the early hours of the night" after Mabel Greineder was found dead, meticulously photographing her clothing and body to record spatter patterns and other forensic evidence.

Martin then described the crime scene as he first found it. When he arrived, he testified, he found "a blood-stained area … a pool … that had leached into the ground." Then, he testified, he noticed drag marks going through the stain, suggesting the body had been tugged along.

The scientist told the jury that blood smears on Dirk Greineder's green and blue windbreaker — what he called "transfer stains" — could have been caused when Greineder picked up and dragged his wife after killing her. One particular smear on the left sleeve, he said, suggested her bloodied head had rested on the jacket.

"That's a 'hair type swipe,'" he testified. "If I were to take some blood and put it into one's hair, what would result would be this type of stain."

The transfer stains themselves alone are not damaging pieces of evidence. The defense claims that Greineder's jacket was stained because he tried to help his wife when he found her beaten.

"If I am lying there bleeding," Martin admitted, "It would be reasonable that a person that comes over to give me aid would have transfer stains."

But Martin also testified that he found impact stains on Dirk Greineder's jacket as well. To drive home his point, he pounded his fist against his palm, repeatedly.

"Is that consistent with the wearer of the jacket being in close proximity to the incident?" Richard Grundy asked Martin.

"Yes," Martin answered.

Martin also testified that imprints on the murder weapons matched the glove that was discarded near the murder scene. This adds to the DNA testimony already linking the glove to Greineder. Prosecutors are expected to show later in the trial how the glove imprint was also found on a pair of glasses Dirk Greineder was wearing the day of the murder.

In his cross-examination, defense attorney Martin Murphy seemed to stretch for a hole in Martin's testimony, and pushed the witness on whether he had simply speculated that blood from Greineder's hand had seeped through a glove.

"Is it fair to say you performed no test on the fabric of the glove to see if blood could leak through that glove?" he asked.

Martin battled Murphy but was cut off when the attorney forced him to cut his answers short. He admitted he hadn't tested the glove, but smiled when Murphy then tried to dismiss the bulk of his forensics work as speculation. Finally, the attorney called for a break.

The dry, scientific testimony Thursday stood in stark contrast to the lascivious admissions and sex-drenched e-mails brought by yesterday's menagerie of hookers, swingers, and porn site operators.

Throughout the trial, Greineder sat in silence. His stoic mug broke only when during breaks, he mustered a feeble smile at his three children who sat behind him in support.

The jury was released after only a half-day's worth of testimony because Greineder, his attorney, and one juror were ill.

The trial is being broadcast by Court TV and will continue at 8:30 a.m. Friday.