Joseph Mercado

In the novel Murder in Mesopotamia, Mr Joseph Mercado has been a member of the archaeological team excavating at Tell Yarimjah for two years. According to Dr Leidner, Mr Mercado has worked at a well-known museum in New York for years. He is found to be a longtime drug user.

Mr Mercado is described as a "tall, thin, melancholy man" with a "sallow complexion and a queer, soft, shapeless-looking beard".

Mr Mercado often works in the laboratory at the expedition house. On one occasion, Nurse Leatheran goes to the laboratory to get a bottle of acetone, and sees Mr Mercado huddled in a corner, with his head down on his arms, seemingly asleep. That evening, Mrs Mercado accuses Nurse Leatheran, saying that she knew perfectly well that there was a bottle of acetone in the antika room, and just went to the laboratory because she wanted to spy on the members of the expedition team.

When Poirot and Nurse Leatheran go to the dig to see Mr Mercado, he is happy to tell them about his work. Mr Mercado is stung by something, and Poirot rolls up his sleeve so that Nurse Leatheran can look at it. While she is applying iodine on the wound, she notices that his forearm is covered with puncture marks that have been made by a hypodermic needle. Poirot later reveals to Nurse Leatheran that he pricked Mr Mercado with a needle, because he had suspected that Mr Mercado took drugs, but needed to be sure.

During the denouement, Poirot reveals that Mr Mercado is a drug user, and is in an advanced stage of the craving. He explains that Mrs Mercado has seemed afraid and worried because she was worried for her husband. He suggests that there may have been some event in Mr Mercado's past that he and his wife had succeeded in covering up, and which would end his career if revealed. Poirot further suggests that if Louise Leidner had learned of this secret, it might have provided the Mercados with a motive for her murder. However, it is never confirmed whether Poirot's suggestions are correct.

Portrayals
In the ITV 2001 TV adapatation of the novel, the part of Joseph Mercado is played by Alexi Kaye Campbell. He has a slightly large role here. At the beginning of the episode, he is seen trying to buy some drugs from a drug peddler named Izzat Baqui. When the price is too high, Mercado murders him instead. Later at the dig, the brother of the murdered man, who is one of the workmen, attacks him and wants to take revenge. Superintendent Maitland and his men are there and they overpower the attacker. Mercado tells Maitland that he doesn't know what the man is talking about--he must be mad, he insists. Later, Mercado leaves the dig and checks into a hotel in Baghdad and shoots himself.