A manic depressive for several years, he prepared the ground thoroughly, first by becoming a member of the Deutsche Gesselschaft fur Humanes Sterben (German Society for Humane Dying) and then by reading up on its 40 different suggestions for how best to commit suicide.
The one he selected was 'Combined method 2: sleeping tablets and bath water' and, in late March, on a day he knew his wife would be out, he finally put the plan into action.
Having read the society's brochure, Dignified and Responsible Dying, Mr Schmitz was confident that within 20 minutes of taking the tablets he would gently slide into unconsciousness and then into death. He decided to record the whole experience on video. So it was that thousands of Germans watching a news programme this month saw Mr Schmitz suffer horribly as he writhed and retched in the final minutes before drowning in his bath.
The society, and particularly its president, Hans Henning Atrott, are alleged to have provided misleading information about methods of dying, to have distributed literature to people who were mentally unbalanced and to have sold cyanide capsules and other lethal medication to willing victims at exorbitant prices.
'We have a lot of opponents,' Mr Atrott admitted in the business-like surroundings of the DGHS headquarters in Augsburg. 'The church condemns us on moral grounds and we are persecuted by fanatics. But we have a lot of supporters too. And we provide a very worthwhile service.'
Since its formation in November 1980, the society has witnessed a spectacular rise in membership, which stands at just over 60,000. In addition to its Augsburg base, it has opened regional offices in Berlin, Hamburg, Dusseldorf, Frankfurt and Stuttgart and it boasts a full-time staff of 22 with more than 100 voluntary helpers.
Mr Atrott is confident, moreover, that the society will continue to expand as more and more people exercise what he believes should be their inalienable right to determine exactly when - and how - they die.
'Our members are on the whole well-educated people who know exactly what they are doing when they come to us,' he insisted.
'They are people who have strived for a high quality of life and all they want is to have a similarly high quality death.'
Mr Atrott's conversion to the cause resulted from experiences in the 1970s working with helicopter rescue teams whose aim was to save the lives of people involved in severe road accidents.
'A lot of the people we saved were subsequently so badly maimed that they openly told us they would have preferred it if they had been left to die,' he said.
Despite unease in Germany over the whole concept of euthanasia (the word is not even used here), the society's membership, after a slow start, rocketed in the mid-1980s after a number of highly publicised suicide cases involving people either incurably ill or almost totally crippled following horrific accidents.
The actress Inge Meysel - referred to as the Mother of the Nation - and a surgeon, Professor Julius Hackethal, were just two of the prominent people who lent support to the DGHS and Mr Atrott, who overnight became something of a media star. Opinion polls showed that 70 per cent of the population agreed with the society's methods and philosophy.
But then questions began to be asked. Professor Hackethal, who had actually joined Mr Atrott in helping a cancer sufferer kill herself with cyanide in 1984, accused him two years later of charging people wanting to commit suicide hundreds of pounds for lethal doses of cyanide, which can be manufactured relatively easily at a minimal cost.
Swallowing cyanide is a particularly nasty way to die, involving suffocation and intense burning pains in the stomach that usually last some 15 minutes.
Although Professor Hackethal lost the court case, concern over Mr Atrott's methods grew and several founding members of the DGHS left the society.
Despite criminal investigations since, the German justice authorities have not pressed charges against Mr Atrott. Committing suicide is not a crime in Germany, nor is assisting someone to do it. However, helping people who are mentally unstable to kill themselves is an offence, as is selling cyanide.
A new investigation has been launched by the Munster state prosecutor's office into the suicide death of Klaus-Peter Rudorf, a notary, in July last year. Mr Rudorf, who mistakenly believed he had Aids and who was undergoing psychiatric treatment at the time, died after swallowing a cyanide capsule.
A former employee has claimed that Mr Atrott was involved in numerous illegal cyanide deals stretching over several years.
Her claims, like others concerning his methods, are dismissed with contempt by Mr Atrott, who alleges that all those prepared to give evidence against him are police spies who infiltrated his organisation. He denies, too, knowingly distributing the society's literature to mentally ill people, arguing that all would-be members have to sign a declaration of sanity before they are allowed to join.
Whatever the outcome of the Rudorf case, Mr Atrott argues that many mentally ill people are actually capable of taking a rational decision to end their lives - and that they should have the right to do so.