The two doctors along with an administrator who work at Bangkok's private Vajiraprakarn Hospital allegedly conspired to sell the kidneys to wealthy transplant patients.
According to local newspaper reports, Dr Siroj Kanchanapanjaphol, a former director of the hospital, Dr Weeradej Lertdamrongluck and Nanthawit Thongchai are not currently accused of actively causing the patients' deaths, but rather failing to observe guidelines for declaring them legally dead.
Earlier this year, the Thai Medical Council revoked the doctors' licences, after finding them guilty of breaching medical ethics by illegally trading in human organs and paying off relatives to convince them to allow the transplants.
Government prosecutor Anuchart Kongmalai says the doctors allegedly murdered the patients in 1997, harvested their organs and faked paperwork to cover up the crime.
Organ payments
Police investigators say the doctors were paid almost one million baht ($25,000) in each case by patients needing organ transplants.
According to some reports police dropped charges against a fourth suspect whom they plan to use as a witness.
The men have denied the allegations, and have been granted bail while the attorney-general considers whether to proceed with formal charges against them.
Dr Siroj told Thursday's edition of the Bangkok Post newspaper that he was confident the charges would be dropped after his explanation was heard.
Organ donation is permitted in Thailand, with the consent of the donor's family and the recipient's - but no money is allowed to change hands.
If found guilty, the three men could face the death penalty.
The attorney-general, who says he has more than 3,000 pages of evidence to sift through, say he will decide whether to proceed with charges on or before 4 October.