ZERMATT, Switzerland — The mystery dates back a century and a half. To be precise, on Tuesday 150 years will have passed since the first triumphant ascent to the summit of the Matterhorn, that legendary bent megalith that towers above the border of Italy and Switzerland. And it was just one hour after that history-making achievement in 1865 that four of the seven climbers fell to their deaths.

Was murder involved, or criminal negligence, as local gossip has maintained ever since? Or was it just an accident complicated by strong personalities and a clash between a well-off British mountaineer and two illiterate local Swiss-German guides?

To anyone arriving in Zermatt this week, the storied resort at the foot of the one of the world’s most famous peaks seemed to be celebrating famed British mountaineer Edward Whymper’s achievement on July 14, 1865. On Monday, tourists paused by the rushing waters of the River Vispa, gazing up in awe as lights marking Whymper’s path up the Matterhorn illuminated the mountain, which was bathed in a gorgeous mauve sunset.