The first degree murder trial of Louise Woodward, the 19-year-old British nanny accused of killing an eight-month-old baby in her care in Boston, is not for the fainthearted. A parade of medical experts has given excruciating detail of the horrific injuries suffered by Matthew Eappen, who died from intra-cranial haemorrhage, or bleeding in the brain.

At the start of the trial this week, Gerard Leone, the prosecuting attorney, set the tone in a powerful and vivid opening statement that had several women in the audience wiping away tears.

He told the 12 jurors and four alternates that Matthew's brain was so swollen that it popped up "like a loaf of bread" when doctors cut into his skull. A doctor later described how blood sprayed all over his tunic during the emergency operation. The court has seen a series of CAT-scan images of Matthew's brain and a take-apart model of a brain.

The prosecution asserted that Woodward, from Elton in Cheshire, was "trapped in a frustrated, unhappy, resentful rage" that led her to kill Matthew by shaking him violently and "slamming him violently against a hard surface". The best evidence, said assistant district attorney Leone, was the "bruised, broken and battered body" of Matthew Eappen.

The prosecution portrayed Woodward as a "party girl" who loved to go out to the theatre with friends and who was frustrated with her duties at the Eappen home. She resented having to look after Matthew and Brendan, his two-year-old brother, for the same pay as other nannies taking care of just one child, the prosecution alleged.

Mr Leone also said that Woodward stayed out late and had trouble getting up.

On one occasion, Woodward allegedly told a couple of strangers while queuing up for tickets for the musical Rent, that her charges were "fussy, cranky, crying little brats". A few days before the tragic incident that has effectively ruined the lives of both families, the Eappens and Woodward agreed to a set of written guidelines in which her "primary goal while working is the safety and well-being" of the children.

But on February 9th, Matthew Eappen died, setting into motion a high-profile trial that has attracted wide notice on both sides of the Atlantic.

Court TV, a US cable channel, carries live coverage, while British stations such as the BBC, ITN and Sky also have teams at the Middlesex Superior Court in Cambridge, Massachusetts.

For American viewers, the Woodward case is a real life version of The Hand that Rocks the Cradle, a B-movie about a murderous nanny. For British audiences, the case raises questions about the American justice system.

Woodward was denied bail and is being tried for first degree murder - defined as an act committed with premeditation or extreme cruelty - despite an absence of any previous criminal record. If found guilty, she faces life imprisonment without parole.

The case evokes every parent's fear that things could go horribly wrong when a child's welfare is entrusted to a stranger. It also conjures up feelings of "middle-class guilt" among parents, forced to devote time to careers at the expense of their children. Class resentment could also come into play. The Eappens are a well-off family, while the jury is mostly blue-collar.

The jurors could side with Woodward as an underpaid teenager, exploited by a comfortable middle-class family living in the prosperous Boston neighbourhood of Newton. Matthew McCue, who is acting as a spokesman for the family, has suggested the class issue could work against his friends.

"There's a very disturbing backlash against Sunny and Debbie Eappen because they are doctors and live in Newton," Mr McCue said.

Woodward, pale and thinner than when she pleaded not guilty in April, is scheduled to take the stand before the end of the trial, which is expected to last just another two weeks. The proceedings have been overseen by the no-nonsense Judge Hiller Zobel.

In the first week, Barry Sheck, on Woodward's defence team, dominated proceedings with masterful cross-questioning of medical experts. Sheck showed why he was picked for O.J. Simpson's defence "dream team".

The youthful-looking but intense New York attorney was purposeful, demonstrated a complete grasp of highly technical medical details and was riveting to watch. The defence's main argument is that Matthew suffered from a pre-existing undetected brain injury which needed little to aggravate it.

So a little shaking, as Woodward admitted to doing, could have precipitated the fatal train of events. The discovery of a broken wrist when Matthew was X-rayed lends some credence to the defence's theory. Mr Sheck has yet to raise the issue of how Matthew got these previous injuries, but is likely to argue that Matthew suffered an accident some weeks before his death.

In one dramatic exchange with Dr Kenneth Mandl, who examined Matthew, Mr Sheck asked whether the doctor had seen any bruises on the baby's arms, shoulders, ribs, abdomen, neck, back or either leg. "No," came the reply in each instance.

But Mr Sheck, who has been doing most of the questioning, has not had everything his own way.

Mr Leone, whose short-cropped hair and ramrod-straight posture makes him look like a marine, scored points for the prosecution when doctors said that Matthew's injuries were caused by someone "swinging and shaking" his head and striking it against a "blunt surface".

Dr Joseph Madsen, who performed emergency brain surgery on Matthew, rejected the contention that the infant had suffered a previous injury. He said that the injuries he saw that day, including a fractured skull and a blood clot, probably occurred only hours before his admission to hospital at four that afternoon.

"It most likely happened one to three hours before we saw him. But that is only an opinion," Dr Madsen told the court. As for the skull fracture, Dr Robert Cleveland, a paediatric radiologist, said that he could not determine how old the skull fracture was. "It has not been there for a long time because the edges are still sharp. But how long I can't tell," he testified.

Throughout most of the week, Woodward, her hair in a ponytail, listened impassively to the proceedings, gazing either at Mr Sheck or the witnesses.

But she was visibly upset on the first day as the court strained to hear the crackly recording of her 911 call to the police, pleading for help for Matthew. She was heard to say: "Help . . . he's making gurgling noises . . . Help, what should I do? . . . I think he puked. His face is going violet . . . Oh my God."

One of her lawyers, Andrew Good, put a comforting arm around her.