Keriako Tobiko, the public prosecutor, offered revenge as the motive at the start of the trial of Thomas Cholmondeley, 38, on Monday and accused Cholmondeley of trying to cover up the crime.
Cholmondeley, who says he fired in self-defence, faces the death penalty if convicted in what is the second time in just over a year that he shot dead a black man on Soysambu, the family's 40,000-hectare farm.
"The accused attacked the deceased and his companions as retaliation or revenge for trespassing and poaching," Tobiko told the hushed courtroom in the capital Nairobi.
Cholmondeley's father Lord Delamere and his wife Ann were among family and friends in the packed panelled courtroom at Kenya's High Court for the trial, which was expected to last five days.
Sitting six metres away was Sarah Njoya, widow of the man Cholmondeley shot. She made no eye contact with Cholmondeley or his relatives.
Educated at Eton, one of Britain's most exclusive schools, Cholmondeley showed no emotion as prosecutors outlined their case against him. He sat with his legs crossed and hands firmly clasped.
Fred Ojiambo, the Cholmondeley's attorney, said in May when his client was charged that Cholmondeley was out walking with a friend on his estate when they came across a four men carrying a dead impala.
He said the men unleashed several dogs and Cholmondeley fired in self-defence, hitting 37-year-old Robert Njoya, a father of two and stonemason by trade, who died en route to a hospital.
Cholmondeley was arrested along with rally driver Carl Tundo after he phoned the police to tell them about the shooting.
White landowners complain about increasing crime and say they feel threatened on their isolated holdings. But on Monday, the prosecutor dismissed such explanations.
"The accused was not under any attack or threat from the deceased or any of his companions. In an attempt to conceal his crime or hinder investigations the accused tampered with the scene after shooting the deceased and two dogs," the prosecutor said.
The prosecution called Peter Njugna, who testified that he and Robert Njoya and another man found a gazelle trapped in a snare on Cholmondeley's ranch, and gutted it. They then heard gunshots and were separated as they fled.
Cholmondeley being escorted to
high court to answer charges
When Njugna and the third man arrived at Njoya's house and did not find him, they told his wife they thought he might have been arrested, Njugna said.
Last year, a murder case against Cholmondeley was dropped after high-level government intervention, enraging Kenyans who say he received special treatment.
Cholmondeley said he mistook an undercover game warden for a robber in that shooting.
Both cases have exposed deep tensions about the British presence in Kenya, with many citizens resentful that the best land was taken over by the British government during colonial times.
After independence in 1963, many departing settlers transferred land to Africans, with Britain underwriting some of the costs.
Some settlers, including Cholmondeley's family, kept their land and became Kenyan citizens. But now, an increasing number of Kenyans are saying the land simply doesn't belong to whites.
Cholmondeley, the only heir to the vast estate in the heart of the Rift Valley - dubbed "Happy Valley" because of the decadent lifestyles of its colonial settlers.
He is the great-grandson of the third Baron Delamere, one of Kenya's first major white settlers more than a century ago.
"The accused was not under any attack or threat from the deceased or any of his companions."
His grandfather, the fourth Baron, was part of the hedonistic "Happy Valley" set of the 1940s.
The group of playboys and aristocrats, centered around the Muthaiga Country Club, outraged society with their promiscuous behaviour, which was exposed to a shocked British public in the 1941 murder trial of Sir Jock Delves Broughton.
Delves Broughton was accused of murdering the 22nd Earl of Erroll. Erroll's affair with Delves Broughton's wife Diana had scandalised white Kenyan society.
The trial was dramatised in the film White Mischief.
Delves Broughton was acquitted.
He committed suicide by taking a drug overdose in his Liverpool hotel room a year later.
The final twist came when, in 1955, his widow married Cholmondeley's grandfather.