Joan Wells Root, 69, the daughter of a colonial-era British settler, was on Friday shot three times in her bed at her home in the town of Naivasha in Kenya's central Rift Valley, where she was raised and had lived for many years promoting environmental causes.

Naivasha police commander Simon Kiragu said two people have been arrested as detectives pursued various leads into the crime.

"We are holding two people as we follow some leads with the aim of uncovering the heinous murder," he said.

The two were arrested after a sniffer dog followed their scent from the compound where Root lived, about 90 kilometers (55 miles) northwest of Nairobi, to a village where they were hiding, Kiragu said.

Nine other people who worked at the slain woman's compound have given statements to police.

After Root's murder, detectives carried out a swoop in the nearby crime-infested Karagita slum and arrested 21 people.

"The group was questioned at the Naivasha Police Station to determine whether they were involved in the murder," police said, adding that the 21 are being subjected to general interrogation although they have not been linked to the murder.

While burglaries are a frequent in the area, police said nothing was taken from the scene of crime and the motive for the killing was not yet known.

Investigators recovered seven AK-47 shell casings at the scene, where Root was shot twice in the leg and once in the hip area and had bled to death as she crawled to her bathroom.

Root, the daughter of Edmund Thorpe, a coffee farmer and photo safari guide who moved to Kenya in 1929, was well-known in Naivasha for her conservation efforts and kept several species of animals, including waterbucks, dik diks and birds, on her compound where hippos were known to gather, residents said.

With her ex-husband, Alan, she made several acclaimed films in the 1960s, 70s and 80s documenting Kenya's stunning wildlife and landscape, and had been active in trying to preserve Lake Naivasha, the Rift Valley's only freshwater lake.

Naivasha has been rife with animosity between foreign investors, mainly flower farmers, and the local population over access to resources, and has been the scene of violent attacks on European residents, although Root's murder is the first in several months.

At least three other Europeans have been slain in violent robberies in the Rift Valley since September 2004, prompting great unease and major security fears in the community.

Amid the heightened security concerns, a prominent British aristocrat, Thomas Cholmondeley, son of the 5th Baron Delamere, shot and killed an undercover game warden on his Rift Valley ranch but escaped a murder trial, insisting he acted in self-defense.

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