BERLIN - Yes, he has investigated cases of murder by poisoning, says Burkhard Madea.

The forensic pathologist at the University of Bonn, an expert in unexplained causes of death, recalls "a series of deaths about 20 years ago when a nurse deliberately gave old, helpless patients the wrong medication. The victims all died suddenly, but there was only one autopsy.” When the procedure revealed that the victim had been poisoned, five other bodies were exhumed; autopsies revealed they had all been murdered.

Poisoning deaths can be established years after a person dies. Skeletons and body residues can shed light on a person’s death long after it occurs. The subject is topical in light of on-going examinations of Palestinian leader Yasser Arafat’s remains.

Twenty years after his death, former Turkish president Turgut Özal was also recently exhumed. Prosecutors ordered the procedure after witnesses reported suspicious circumstances surrounding his death.

Turkish newspaper Today’s Zaman reported last week that experts at the Adli Tip Kurumu Institute of Forensic Sciences had found four toxic substances in Özal’s remains, including high amounts of DDT and traces of radioactive polonium.

"Finding traces of poison in the remains of somebody who’s been dead for a long time depends strongly on just how long, and under what conditions, the person has been in the ground," Dr. Madea says. A corpse in cool, dry conditions is usually better preserved than one in wet or damp conditions. Dr. Madea adds that experts also always take soil samples in case the substances stem from the soil.

And of course the poisons still have to be in the remains – "traces of substances like gas or narcotics that are inhaled disappear very quickly," says Dietrich Mebs, a toxicologist at the University of Frankfurt for over 40 years.

It is different with radioactive poisons like the polonium that was used to kill Russian secret agent Alexander Litvinenko in 2006. Depending on the decay period and dosage, their presence can be proved long after death.

"In the 19th and 20th centuries, arsenic, thallium and E605 parathion were often used," says Madea. "But they’re not so widely available anymore, so you don’t see them used in murders anymore."

Proof is in the pudding

Dietrich Mebs remembers an attempted murder case from 30 years ago." A man wanted to poison his wife, so he mixed cyanide in her pudding but it smelled so awful the wife realized what was going on and called the police. They brought us the pudding to test."

However, without suspicion of foul play in a person’s death, there is no forensic examination. And if there is suspicion, the lab work has to be rigorous. "In forensic medicine and specialized labs, ways of proving the presence of poison are getting ever more refined," says pathologist Madea.

"You can detect tiny amounts of poison and then calculate how much the person had in their body at the time of death – and if in fact the poison could be a cause of death." This applies to both artificial substances as well as natural poisons.

Substances in the tissues are examined using high-pressure liquid chromatography or mass spectrometers. "Once I had a case where a man used snake venom to kill his mother-in-law,” says Mebs.

"The woman, who was quite old, had a fixed stare, and then suddenly died. Nothing unusual at her age, except that neighbors had observed that the son, who was not on good terms with her, had been hugging her a lot lately."

That seemed so unlikely that it aroused suspicion and an autopsy was conducted that revealed a pinprick hole in the woman’s shoulder. "The police found the equipment the man used to prepare the poison in his apartment."

Euthanasia – or poisoning?

A relatively new phenomenon is poisonings in hospitals and nursing homes – and, apparently, they aren’t all that rare. Since the 1970s, there have been many cases where nurses have killed off their patients out of greed or for attention. "All a nurse has to do, for example, is increase the dose of a patient’s blood-pressure medication; the patient will die from drug overdose," explains Dr. Madea.

Cases of poisoning in clinic or nursing home circumstances are particularly challenging to criminologists – as they are exceptionally hard to solve. Sick, older patients may be taking a great deal of medication, with many different substances. Both patients and those looking after them can easily lose oversight, making the situation easily exploitable. "But you do need the requisite amount of knowledge to do so successfully," Mebs points out: "Luckily, not all too many people possess it."

Mebs also points out that new medication is generally safer than older preparations. "Modern sleeping aids, for example, don’t contain any derivatives of barbituric acid so you can’t use them to commit suicide, much less kill someone. That ingredient in first generation sleeping aids led to many accidents and deaths. To all intents and purposes, modern sleeping aids are non-toxic.”

Murder by poison has traditionally been considered a favorite for women killers. However, says Dr. Madea: "Just as many men use poison to kill as women do.” Although there are no precise figures, "it is estimated that every year about 1,000 murders go undetected as such, and a large portion of those are probably murders by poison."

The only way to fight that, he says, is for doctors filling out death certificates to pay closer attention and particularly with older patients not simply automatically write “death from natural causes.”