CAMBRIDGE, Mass. (Court TV) — The day after Christmas began quietly at Edgewater Technology, an Internet consulting firm in the Boston suburb of Wakefield. Many of its 240 employees had taken Dec. 26, 2000, off and those who were at their desks counted on a relaxed day.

All, that is, but one man. Michael McDermott, a burly 42-year-old software tester, rose from his chair just after 11 a.m. with a rifle, a shotgun and a pistol in his hands. Over the next seven minutes, he stormed through the office, fatally shooting seven co-workers.

When police arrived, they found McDermott seated in the lobby, surrounded by his weapons and the bloody bodies of two of his victims.

Officers ordered him to disarm, and he matter-of-factly replied: "I don't speak German."

McDermott goes on trial for seven counts of murder this week in Cambridge. His defense lawyer doesn't deny the 6-foot, 2-inch Navy veteran pulled the trigger, but claims McDermott has a long history of schizophrenia and depression and was insane when he committed one of Massachusetts' worst mass killings.

Prosecutors, however, maintain McDermott knew exactly what he was doing. They say he planned the killings in revenge after his company began cooperating with the IRS in garnishing back taxes from his paycheck.

If jurors reject the insanity defense and convict McDermott, he faces life in prison.

The Killings

On Dec. 26, McDermott arrived as usual to Edgewater's offices in a red-brick converted mill. He had worked for the company for nine months, earning an annual salary of about $55,000. With long busy hair, a full beard, and a hulking 260-pound frame, McDermott was regarded by colleagues as quirky but not dangerous.

Authorities say that at 11:10 a.m. McDermott picked up a gun bag stashed in his work area and muttered something about going to the human resources department. He set out for the company lobby, at some point stuffing a semi-automatic pistol in his pants pocket and carrying a 12-gauge pump-action shotgun and an AK-47 semi-automatic rifle.

In the lobby, he encountered Cheryl Troy, 50, the human resource director, and Janice Hagerty, 46, the office manager. Authorities say he shot Troy five times and Hagerty twice and then moved onto the mezzanine where he hit Louis Javelle, 58, the director of consulting, with three bullets.

According to prosecutors, he then moved through the offices, shooting Craig Wood, a 29-year-old who worked in the human resources department, five times, and Jennifer Bragg-Capobianco, also 29, four times. Both died at their desks.

Finally, authorities say, he tried to get into the accounting office where three employees had barricaded themselves. He blasted through the door and killed development technician Paul Marceau, 36, with six shots and payroll accountant Rose Manfredi, 48, with five.

A third employee managed to conceal herself by crawling under her desk and pulling her chair, trash can and leather coat around her. The woman says she heard Marceau begging McDermott for his life, and then more gunshots.

According to police, McDermott then returned to the lobby, laid his two long guns down and waited for police.

"As the officers approached him with weapons trained on him, McDermott did not move his body. He only followed the officers with his eyes," according to Middlesex Assistant District Attorney Thomas O'Reilly.

At that time and once later as he was being booked, McDermott cryptically declared "I don't speak German."

McDermott had emptied his the long guns, firing at least 55 times. Police found the loaded pistol still in his pocket.

A search of his work area revealed 28 boxes of ammunition, a bayonet, another rifle and a letter from the IRS. In his apartment were bomb-making chemicals and blasting caps.

Prosecution's Theory: Careful Planning, Obvious motive

Prosecutors are expected to portray the crime as carefully planned and malicious, the work of a quietly seething man, not a mentally disturbed one. Middlesex County District Attorney Martha Coakley has said many of the victims were specifically targeted because of a small role they played in McDermott's long-running dispute with the IRS.

Before the holidays, McDermott learned that Edgewater planned to turn part of his paycheck over to the IRS each pay period to settle his back taxes. According to prosecutors, McDermott owed the government about $5,000.

The company agreed to hold off on garnishing the funds until after the holidays. The week before Christmas, McDermott allegedly clashed with Manfredi and other co-workers in the payroll department. With the company set to begin deducting the IRS debt from his paychecks, leaving him with a weekly take home pay of $275, he asked for an advance and a raise. Manfredi refused.

After the shooting, her mother told the Boston Globe that her daughter talked about being frightened of McDermott in the wake of their argument.

McDermott reportedly also owed money to his prior landlord and his car insurance agency. Prosecutors are expected to argue that with the bills piling up, he made a deadly plan.

On Christmas Eve, some residents of the town of Haverhill, where McDermott lived, called police to report a man firing a gun. When officers went to the scene, they found shells in the road and a witness who described a big man in a car with the vanity license plate "MUCKO" — the nickname McDermott's nieces and nephews gave him when they could not pronounce his name.

Haverhill police traced the plate and visited McDermott's apartment several times on Christmas day to question him, but they did not find him home. In fact, prosecutors say, McDermott was busy having dinner and exchanging gifts with his girlfriend and family.

But in the midst of the festivities, prosecutors say, McDermott had his mind on bloodshed. They claim that after dropping his girlfriend off Christmas night, he used his pass card to enter the darkened Edgewater office. There, they say, he stashed weapons and ammunition at his desk, preparing for the next day's carnage.

The morning of Dec. 26, McDermott received a letter about his 1994 Plymouth. He was behind in payments, the financing company told him, and they were repossessing the car.

"I won't be needing it, come pick it up," he told the customer service representative, according to the Boston Globe.

Three minutes later, he began shooting.

The Defense: Mental illness, heavy medication

McDermott's lawyer, Kevin Reddington, will present McDermott as a seriously mentally ill man who could not understand his own actions. The defense lawyer has suggested the psychiatric medications McDermott was taking, including Prozac, might have been a factor in the killings.

Three psychiatric witnesses as well as McDermott's relatives are expected to describe him as suffering from schizophrenia and depression for years leading up to the shootings.

In court papers filed last month, Reddington said the expert testimony about the schizophrenia diagnosis is so important that jurors should be allowed to submit questions in writing for the witnesses.

"Since schizophrenia is a complicated brain disease, it is essential that jurors understand the complexities in order for them to reach a verdict supported by the evidence," Reddington argued. The request was denied.

McDermott, born Michael McDermod Martinez, is the son of two well-respected retired school teachers. He changed his name in 1982 to McDermott, reportedly to sound Irish rather than Hispanic.

After high school, he entered the Navy and served six years as an electrician aboard a nuclear submarine. After receiving an honorable discharge from the Navy, he began working at the Maine Yankee nuclear power plant in 1982.

In an interview with the Globe, his parents said they had a family history of depression and their son suffered the first of several mental breakdowns while working at the power plant. In 1987, he attempted suicide. He later filed a workers' compensation claim against the power plant, citing his "stress induced suicide attempt." He was fired from the plant the next year.

He found another job in research at Duracell, but in Feb. 2000, he left and took a job at Edgewater.

McDermott's five-year marriage to his childhood sweetheart, Monica Sheehan, ended in divorce in 1997.

His parents said they knew he was being treated for depression and on several medications, but were unaware he was having financial problems. Rosemary Martinez said the family enjoyed a happy but uneventful Christmas the day before the shootings.

"We had the most wonderful Christmas with him," Martinez said. She said McDermott seemed fine then as well as the next morning, when she spoke to him on the phone about an hour before the shootings.

"I talked and laughed with him at 10," she said.

Burden of Proof

Under Massachusetts law, McDermott is not criminally responsible for the shootings if mental illness prevented him from "(appreciating) the wrongfulness or criminality of his conduct or (conforming) his conduct to the requirements of the law."

It is up to the prosecution to prove beyond a reasonable doubt that McDermott was sane during the shootings.

— The Associated Press contributed to this report.