In 1981, Frei was suffering from chronic acid reflux, stemming from a hiatal hernia, a very uncomfortable but essentially low risk condition.
At the time, Dr Larrain was a world-renowned gastric surgeon, as well as a cousin of Andrés Zaldívar, one of Frei's closest advisers.
After Belgian researchers from the University of Ghent reportedly found biological remnants of mustard gas in Frei's body, the former president's family filed a lawsuit, which is still pending as of 2009.
[3] Judge Alejandro Madrid based his decision on a report that determined that Frei was administered low doses of thallium and mustard gas over an extended period while he was hospitalized at the Santa María Clinic in Santiago and that these toxic substances had the effect of decreasing Frei's immune system, making him too weak to survive his surgery".
[6] In April 2013, the body of poet Pablo Neruda, who died in the same hospital one day before departing for exile, was exhumed amid suspicious of foul play in his death.
On 25 January 2021, the convictions would be overturned by a Chile Appeals Court three judge panel which found that Montalva was not a homicide victim.