A Form Four student of Ruthagati Boys’ High School in Mathira West, Nyeri County, was found dead in a dormitory on Saturday morning.
Charles Munari, Mathira West Deputy County Commissioner, said another student found the body of Mwai Gitonga on the floor of the facility.
The student alerted the watchman who then informed the school's authorities.
"The deceased had not complained of any ailment and had studied with his friends the previous night," he said.
Mr Munari said preliminary investigations ruled out suicide, which had been suspected.
"We are still trying to get to the bottom of the incident. The Directorate of Criminal Investigations has taken over in a bid to establish what exactly caused the death."
The school's principal did not answer phone calls for comment on the incident and reports indicated that he was away.
The body was taken to Karatina Level Four Hospital mortuary.