Professor Lemos is a forensic toxicologist with experience in the determination and interpretation of alcohol, drugs and poisons in biological fluids and matrices as well as their interactions and effects in both postmortem toxicology cases as well as human performance toxicology cases.

Professor Lemos' formal education includes:

Bachelor of Science in Criminalistics (State University of New York, USA, 1993)

Master of Science in Forensic Science (John Jay College of Criminal Justice, USA, 1996)

Doctorate in Forensic Medicine and Science (University of Glasgow, UK, 1999)

Currently, Professor Lemos holds the following appointments:

Director, Forensic Laboratory Division, Office of the Chief Medical Examiner, City and County of San Francisco

Chief Forensic Toxicologist, Forensic Laboratory Division, Office of the Chief Medical Examiner, City and County of San Francisco

Examiner, Pograduate Diploma in Forensic Medical Science, The Worshipful Society of the Apothecaries of London.

Clinical Professor (WOS), Department of Laboratory Medicine, School of Medicine, University of California, San Francisco.

Professor Lemos has served on numerous occasions as an expert witness in response to requests from both the prosecution as well as the defense in the United Kingdom and the United States of America for more than a decade. He has consulted on and testified in cases pertaining to death investigations, drug-facilitated sexual assaults, hit-and-run offences, driving under the influence offences, public intoxication offences and several other types of offences.

He has been qualified as an expert in forensic science, forensic toxicology, postmortem toxicology, human performance toxicology, on the effects and interactions of alcohol and drugs on human behaviour and on the interpretation of blood, urine, hair and other tissue drug and alcohol levels both in the United Kingdom and the United States of America.

Professor Lemos remains active in all aspects of forensic toxicology and is currently affiliated with the following professional organisations and societies:

• Fellow, Royal Society of Chemistry
• Fellow, American Academy of Forensic Sciences
• Member, The International Association of Forensic Toxicologists
• Member, Society of Forensic Toxicologists
• Member, British Academy of Forensic Sciences
• Member, California Association of Toxicologists
• Member, California Association of Criminalists
• Member, American Chemical Society
• Member, American Society of Crime Laboratory Directors
• Affiliate Member, National Association of Medical Examiners

Professor Lemos is often invited to be a peer reviewer for various scientific journals in forensic sciences including The Journal of Clinical Forensic Medicine, Science and Justice, the Journal of Forensic Sciences, and the Journal of Analytical Toxicology.

Since 2011, Professor Lemos  is a Diplomate of the American Board of Forensic Toxicology (D-ABFT).