PETRA Diamonds said it was investigating allegations by a British non-governmental organisation that subsistence miners who trespassed on the firm's Williamson mine in Tanzania were detained, beaten and shot at, killing at least seven of them. The RAID report, based on research conducted between September 2019 and November 2020, alleged that security contractors and security employees of Petra's subsidiary Williamson Diamonds Limited (WDL) used excessive force. Petra Diamonds told Reuters a specialist external adviser was conducting an investigation and said an external consultancy had been appointed to assess WDL's management of its security. "The board of Petra Diamonds finds the…