Mr Nyamato said his son was constantly in contact with the family, only to be notified a few days later that he had died.
According to a report that the family received, Nyankieya was found dead in his hotel room in Washington after his compatriots noted that he had delayed waking up.
From the time of last contact with his kin, the family has remained in the dark about the happenings.
"Even if your cat dies in a neighbor's house, you would want to know how it died and at least a convincing account of the incident," said the father.
During the funeral, Mr Nyamato, who was in the presence of government representatives, only said his son died abroad but did not provide any details and restricted himself to the eulogy that was in the printed booklet.
"My son was a smart person who mentored many people especially his siblings in different capacities. He was an honest and devoted servant who has left a legacy to be emulated," said the father.
After the funeral, he told The Saturday Standard that the family had already procured the services of a lawyer as they embark on seeking the truth about the death of Nyankieya, who until his demise was a personal assistant to the Deputy Inspector General of Police Noor Gabow.
Earlier, there was disquiet during the ceremony as both the family and the government failed to share details on the cause of the officer's death.
The burial was a break from normal ceremonies in the region that are complete with testimonies of how the deceased died and what postmortem results indicated.
None of the speeches highlighted how he died and the cause of his death as shared by authorities to his family.
The funeral was attended by the Director Operations, Administration of Police Godfrey Otunge, who represented the Inspector General of Police.
He was one of the officers who were with Nyankieya in Washington DC.
Mr Otunge said he was with Nyankieya in the UN delegation that was preparing for the Haiti mission and mentioned him as a key Kenyan police officer whom he worked closely with in doing presentations during the preparation workshops.
He, however, did not divulge details on his death.
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Family members also avoided talk about the circumstances surrounding his death.
The widow, Regina Wanjiru, who is also a senior police officer in Kitui County, eulogised the late Nyankieya, saying he died at a time when they had a lot of plans to accomplish together.
"We had a lot of plans that are now cut short. I don't know how I'll continue with this journey without you," she said
Nyamira Governor Amos Nyaribo said the country had lost a very resourceful young person.