After a 59-day trial that ended last week, Shipman has emerged as one of Britain’s most prolific serial killers. The charge sheet against him listed 15 middle-aged or elderly victims–all women, few seriously ill. But police have opened investigations on more than 120 other deaths that may be connected to the 54-year-old doctor. In most of the cases, motive remains a mystery: the Grundy killing seems to be the first in which Shipman changed a patient’s will to enrich himself. Yet the absence of even twisted logic to explain the murder spree only makes it seem more bizarre. Jailing Shipman for life, Justice John Forbes told him: “I have little doubt each of your victims smiled and thanked you as she submitted to your deadly ministrations.”

According to statements made at the trial, the doctor typically would call at a patient’s home when she was alone. On the pretext of taking a blood sample, Shipman would inject a lethal dose of diamorphine, then watch as the drug took effect. When his day’s work was done, Shipman would then return to his modest two-story home, which he shared with his wife, Primrose, and four children. Sometime later, he’d be called upon to write up the death certificate. “He was such a nice man,” says Hilary Mason, some of whose family were treated by Shipman. “I thought [the police] must have got it mixed up.”

Yet many other Britons wonder why it took the authorities so long to catch on. The death rate among elderly women under Shipman’s care was three times higher than normal for the area, and a local undertaker had voiced suspicions to another doctor. An implausible number of Shipman’s patients died suddenly in the daytime–and soon after a visit from their physician. (Most of Shipman’s victims were in their 60s or older.) Police did launch an inquiry six months before Shipman’s arrest, but the case was dropped for lack of evidence even before the suspect was questioned.

Could stricter supervision and better police work have prevented many of the killings? A government inquiry will have to determine that, among other things. But local coroner John Pollard has doubts: “A doctor is in the ideal position to carry out this kind of murder,” Pollard says. “He has the trust of the patient, the ability to prescribe drugs and the right to sign a death certificate.” Regulations and enforcement may be no match for pure malice.