Four people have been arrested during an investigation into the deaths of 18 elephants in southern Kenya's Amboseli ecosystem.
The suspects have since been released on bail, a Kenya Wildlife Service spokesperson told Reuters. The ministry has not announced their names or any formal charges.
The first 15 deaths were recorded between June 24 and July 24 in Amboseli National Park, Kimana Sanctuary and the Kuku Ranch area. The total had risen to 18 by August.
Preliminary laboratory findings point to a toxic substance as the cause of their deaths. An earlier theory suggested cyanide exposure through pesticide-contaminated tomatoes, but it has not been confirmed.
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Kenya's Ministry of Tourism and Wildlife said the four were apprehended as persons of interest. Investigators are also looking for a fifth person believed to have information relevant to the case.
A search in Tikondo, Kimana, within Loitoktok Sub-County uncovered assorted chemicals and unlabeled materials. Some were believed to have entered Kenya from a neighboring country, and the recovered substances were sent for scientific testing.
Ten of the first 15 elephants showed similar symptoms, including partial paralysis that left them unable to stand. They died within one or two days. Most of the affected animals were adult females and calves, with only one adult male among the initial cases.
The Big Life Foundation said cyanide was detected in samples, but further testing was needed to determine whether the concentration was lethal. The conservation organization also said there was no clear evidence of where the substance came from or whether it was introduced intentionally.
The Amboseli ecosystem includes the national park and surrounding community lands near Kenya's border with Tanzania. Elephants travel across that wider landscape beneath Mount Kilimanjaro rather than remaining inside the park.
Amboseli is one of Kenya's most popular safari destinations and is especially known for its large elephant herds. The Tourism and Wildlife Ministry's statement did not announce any visitor restrictions. The government said it is increasing wildlife surveillance, monitoring potentially hazardous substances and working with communities on both sides of the border.