Elton Smith was convicted of murder, robbery with aggravated circumstances, the illegal possession of a firearm and the illegal possession of ammunition, reports the Independent Online.

His brother Wayne was found guilty of being an accessory to the murder, but was cleared of the killing itself.

The Smiths were arrested and charged in the summer of 2009 after Jonkheid’s body was found in the grounds of a church in the Western Cape town of Stellenbosch.

Jonkheid was the victim of a carjacking and died of a gunshot wound to the head.

He was based in Johannesburg but had travelled to Stellenbosch to attend the annual conference of the South African Marketing Research Association (Samra), where he was a member of the paper judging panel.

At the time of Jonkheid’s death Samra chair Niel Victor paid tribute to “one of our top global strategists and qualitative researchers”.

“Dr Klaas Jonkheid has been a mentor to many and his contribution to the industry was well recognised locally and on the global stage. Many of us will miss his words of encouragement, guidance and motivation,” he said.

Jonkheid founded The Consumer Psychology Lab in 2005 after stints in brand management at Cadbury Schweppes and as head of research and strategy at advertising agency FCB South Africa.

The business remains in operation, led by Jonkheid’s wife Liezel and colleagues Ingrid Olivier and Marianne Engelbrecht.