A group of villagers tracked down Masten Wanjala to a house in Bungoma town, close to the Ugandan border, where he was eventually killed.
He also admitted to giving the boys drugs and, in certain circumstances, to drinking their blood.
Area Assistant County Commissioner Cornelius Nyaribai said Masten Wanjala was killed near his home in Bungoma county, a day after he escaped from police cells in Nairobi.
Authorities said Wanjala was identified after he played with locals in a football match. Some then trailed him and beat him to death.
“The law of the jungle as applied by irate villagers prevailed,” Kenyan police’s Directorate of Criminal Investigations said in a tweet on Friday.
Authorities have said Wanjala confessed to killing children in Nairobi, Machakos and Bungoma when he was arrested in July. He reportedly posed as a football coach to lure victims.
So far, five bodies have been recovered.