A forensic scientist who was due to give evidence at the "Operation Puerto" trial examining Spanish doctor Eufemiano Fuentes' involvement with a number of high-profile cyclists has died, media reported on Tuesday.
Francisco Aguanell passed away on Monday after suffering a heart attack, a number of Spanish newspapers said, quoting unnamed sources and without elaborating as to how he died.
Aguanell was due to give evidence on Wednesday to the trial in which Fuentes is charged with endangering public health by performing blood transfusions.
No-one was immediately available for comment at the court in Madrid when contacted by AFP.
The scientist had examined former cyclist Jesus Manzano after he claimed to have worked with Fuentes and his testimony was expected to be key in determining whether the transfusions had a detrimental affect on the long-term health of his clients.
Fuentes is on trial with his sister Yolanda and three other defendants from cycling teams in one of the most high-profile cases in sport over a blood doping racket, with suspects across the drug-tarnished world of cycling and possibly beyond.
The five are accused of endangering public health but not incitement to doping, which was not a crime in Spain at the time of their arrests in 2006.
A total of 58 cyclists are suspected of involvement in the scandal but only six have been sanctioned by their sport, including two-time Tour of Italy winner Basso.