DEDHAM, Mass. — A somber courtroom heard a recording of the breathless and frantic 911 call that Dirk Greineder made just minutes after his wife's brutal murder in a wooded suburban park.

"Help! Help! My wife's been attacked. I need help," hoarsely shouted the renowned Boston doctor, who is being tried for first-degree murder in the killing.

As the tape was played, Greineder, 60, dabbed at his eyes with a white pocket handkerchief and repeatedly blew his nose. Occasionally, he twisted around and cast mournful glances at his three children, who covered their faces and silently sobbed at intervals throughout.

Kirsten, Britt, and Colin Greineder have all publicly supported their father, who the prosecution says killed his wife of 31 years while on a walk because he wanted to more freely pursue a secret sex life. The defense claims that the couple separated on the walk after she hurt her back. Greineder says he left his wife, Mabel, to go exercise their dog, and found her dead after returning minutes later.

The doctor attempts to explain this sequence of events on the 911 tape, but much of the recording is jumbled and difficult to make out. Shannon Farillo, the police dispatcher who spoke with Greineder, can be heard repeatedly telling the excited doctor to relax and speak more slowly.

Key testimony from dog walker, police

On the third day of testimony, several key prosecution witnesses took the stand, including the detective on the case, the first officer dispatched to the murder scene, and a dog walker who saw Greineder emerge from an area where two weapons used to kill Mabel Greineder were later found.

William Kear testified that he was walking his small terrier in the Morse's Pond park on the morning of October 31, 1999 when he saw Greineder and his dog emerge from a wooded trail, cross a cul de sac, and head down another paved path.

A small hammer and a pocketknife were recovered from underneath a storm drain a short ways down this path. During his opening statement to the jury last week, Grundy repeatedly claimed that doctor disposed of the weapons just before seeing Kear.

Defense attorney Martin Murphy tried to discredit this theory during cross-examination, getting Kear to recall that Greineder claimed to have gone down the path after seeing someone, and prodding him to acknowledge that the doctor may have been out of sight for only about 20 seconds.

The defense lawyer also dramatically held the hammer allegedly used to bludgeon Mabel Greineder, and, slightly swinging up and down like he was going to bang on the podium, forcefully asked, "You didn't see him with a two-pound hammer, did you? This is an object that you never saw that day?"

Kear did testify that Greineder was wearing a small red backpack at the time. A source of considerable mystery in the case, the backpack was never recovered by police.

Speaking slowly and deliberately in a flat monotone, Kear told the jury that he didn't think much at the time of his observations until Greineder came back and approached him.

"The defendant came up to me and asked if I had a cell phone," he slowly recounted. "He said that his wife had been attacked."

Greineder's call for help

Greineder ran out of the park to use a phone in his car, leaving Kear alone near the site of the murder, a situation the man said left him in a quandary.

"My thoughts were whether there was (a killer) in the woods," he said, recalling his uncertainty about how he could help and his fears for his own safety. "What is my moral obligation?"

The man's trepidation was soon alleviated when Officer Paul Fitzpatrick arrived on the scene after being dispatched by the police operator who received Greineder's call for help.

An elderly man in a navy blue blazer with big brass buttons, the officer described accompanying the doctor back to the murder site and his observations afterwards. Driving down an access road to the area in the park where the attack occurred, the officer saw Greineder jogging back to the scene and picked him up.

When they arrived at the murder scene, Fitzpatrick said, the doctor bolted out of the car and ran down a wooded path to where his wife lay. The officer told the jury that when he caught up to Greineder, the doctor was sitting next to his wife and adjusting her pants and her clothes around the chest area.

After other emergency personnel arrived at the scene, Fitzpatrick stood around with the doctor near the crime scene.

"After a while he asked me if she was dead," he testified.

The officer told the doctor that he thought his wife had died, and five minutes later was asked a surprising second question.

"He asked me if I was going to arrest him," Fitzpatrick told the jury.

No blood on his hands

The case detective, Jill McDermott, testified that Greineder had blood on his windbreaker, shoes, and glasses, but none on his hands, when she encountered him near the crime scene. The prosecution claims that the doctor's clean hands are an indication that he wore gloves during the attack.

"He had been pacing off and on. At one point he was laying on his stomach, his elbows down and his head resting on his hands," recalled McDermott.

Sam Sit, a resident who was jogging in the park at the time, took the stand and testified that Greineder seemed more upset than nervous.

"I'm a good doctor. But it doesn't matter how good I am, because I can't save her," he recalled a distraught Greineder crying.

McDermott did not finish testifying and will take the stand again at 9:00 Wednesday morning.

The trial is being broadcast on Court TV.