MANCHESTER, England A public inquiry opens Wednesday into the murderous career of Harold Shipman, the British family doctor thought to have methodically killed hundreds of his patients, AFP reported.

The inquiry, due to start at 0900 GMT, is trying to answer the question probably only the 55-year-old doctor himself knows: How many people succumbed to his lethal syringe?

Convicted over 15 deaths and jailed for life last year, Shipman is already Britain's most prolific mass murderer.

Yet the sheer scale of his deadly reach is almost beyond comprehension. By the time of his arrest three years ago, the death toll at his one-man surgery was averaging one a week.

A government report last year concluded his most likely toll was about 236, but the inquiry chairwoman, High Court Judge Dame Janet Smith, said she would look at 466 cases at his practices over 25 years. Another 152 may also be examined.

Shipman killed his patients by administering a lethal dose of diamorphine, the medical term for heroin.

Most of his victims were elderly women. Most died in the afternoon, in the privacy of their home, without suffering life-threatening symptoms.

And they all died during or just after a call from their trusted doctor.

Another question that can only be speculated about is what his motive was. The bearded, bespectacled doctor, whose patients regarded him as attentive and caring, has refused to admit anything.

He is not expected to attend the inquiry.

The first phase will consider how many he killed, over what period of time and how he did it.

It will then study how he got away with it for so long and what can be done to make sure it could never happen again.

It was only in 1998, when a clumsy attempt to forge a will was discovered, that the threads came together leading to Shipman.

"There will be several hundred deaths in which I can say yes or no," Smith said last week.

"I hope that will bring a sense of closure."

The inquiry, in a converted council hall in Manchester, northwest England, is expected to last well into next year and cost millions of pounds.

But although the real murder toll appears many times higher than the 15 for which he was convicted, he will not face another trial because Britain's State Prosecution Service says his notoriety means he would not get a fair hearing.