Three Thai doctors were acquitted on Tuesday on charges of conspiring to murder patients for their kidneys, after a trial that spanned three years.

The Bangkok criminal court ruled the doctors did not kill two female patients, both then in a coma, for their kidneys because they were brain dead before the organs were removed in 1997.

However, the court said one of the doctors, then the director of the hospital, might have falsified letters from relatives consenting to kidney donations and ordered him detained pending any prosecution appeal, which must be made within 30 days.

Trade in human organs is illegal in Thailand, but some doctors say it has been known for hospitals to tiptoe around the law by transferring dying patients to other hospitals in return for money, some of which goes to relatives of the patients.

Thai law says usable organs can be removed from dying people only if they are declared brain dead.