Ms Ward, aged 28, died while on safari in the Masai Mara game park, and for more than a year the Kenyan authorities denied that she was murdered, saying she had been attacked by wild animals.
The publicity surrounding the case, and several other killings of tourists since, have damaged the Kenyan tourist industry, the country's main foreign currency earner.
An inquest in 1989 found that the police had been wrong to treat the death as accidental, and that a post-mortem report had been falsified by a senior pathologist.
Two men were tried for the murder in Nairobi last year, but were acquitted. The judge recommended the close examination of three other suspects, all workers in the Masai Mara reserve.
Now the Kenyan government has agreed to a new investigation. John Ward, the dead woman's father, said he had been invited to return to Kenya next month to meet the investigating officer replacing Superintendent Muchiri Wanjau, who had headed the case since 1988.