Alain-Deni Lemaistre's wife Carol, of Blackthorn Lane, Bacup, died on January 28 after a battle with colon and liver cancer.
She chose to have alternative treatment, administered by her husband, instead of conventional medical methods.
Police began investigating Mr Lemaistre, 58, of Burnley Road, Todmorden, after they discovered he had no formal medical qualifications but referred to himself as a doctor.
Mr Lemaistre, who calls himself a doctor on his advertising literature, says he gave up a lucrative career in engineering to study chiropractics.
He practises a system of healing called Bio Synergistic Chiropractic from a clinic in Meadow Lane, Todmorden.
The American, who has been ordained as an episcopalian preacher, is not registered with the General Chiropractic Council but says he does not need to be as he is not a chiropractor.
"The police are really shooting themselves in the foot with this investigation," said Mr Lemaistre, who failed to get a chiropractic qualification after studying for four years.
"I don't call myself a chiropractor or a medical doctor. I don't want to be part of the medical profession. I have different beliefs. All I am interested in is what makes people sick and how to make them better.
"I don't give my clients injections or tablets. I just use my hands and my own bio synergistic system."
The father-of-three, who says he studied chiropractics in Bournemouth for four years, combines these skills with reflexology and homeopathy techniques.
"I've treated thousands of clients all over the world and made a lot of people better who could not find relief anywhere else.
"Under Common Law in the United Kingdom, anyone can treat a sick person even if they have no training in any type of healthcare", said Mr Lemaistre, who does not charge for his services but asks for donations.
A spokesman for the General Chiropractic Council said anyone claiming to be a chiropractor who was not on their registration list was breaking the law.
An inquest into the death of Mrs Lemaistre has been opened and adjourned. Inquiries are still being carried out by Lancashire Police's Public Protection Unit.
arlene.lawler@halifaxcourier.co.uk