Joaquin "El Chapo" Guzman was a ruthless killer who ordered the murder of a man who had refused to shake his hand at a meeting, a prosecution witness told jurors at Guzman's U.S. trial on Monday.

Jesus Zambada, the brother of Ismael "El Mayo" Zambada, who was Guzman's alleged partner in running the Sinaloa Cartel, gave his most dramatic testimony after three days on the witness stand as he described Guzman's involvement in a series of murders.

In a cross-examination, one of Guzman's defense lawyers launched an attack on Zambada's credibility, highlighting inconsistencies between his testimony and his original statements to U.S. prosecutors.