Security was tightened in South Africa’s Kruger National Park nature reserve after two tourists were found killed there, authorities said on Sunday.

The two South African victims, a 71-year-old man and a woman whose age was not disclosed, failed to return to their lodge on Wednesday evening, prompting a search operation.

Other tourists eventually found them in a river on Friday afternoon. Police said the man had stab wounds and the woman’s body was bruised. Their car was missing.

The circumstances of the incident remain unclear, and the police have launched two investigations into murder and kidnapping.

South Africa National Parks said it was “deploying additional monitoring and ranger resources in specific areas of concern” in response.

It added that it was “enhancing technology systems to strengthen surveillance and early warning capabilities”.