In a cryptic message posted on the account, Kosgei tagged the Directorate of Criminal Investigations and media stations, warning of his intent to commit a crime.
Within the thread of messages, Kosgei narrated their happy times, from when they began dating in high school to starting a family.
He explained how his wife became pregnant, and they decided to move in together and start a family. He later mentioned that he opted to search for a job while his wife pursued a course in Education.
Cheating
Problems arose when he secured a job in Thika and left his wife in Nyeri. According to Kosgei, his 29-year-old wife, Jackline Kimaiyo, was cheating on him with two men.
"If by any chance something happens, then know what was happening behind the scenes," Kosgei said in one of his posts.
"It has officially ended, guys. Though I am mentally disturbed by the things that she has put me through..." he said.
On the day he posted "Enough is enough," Kimaiyo was missing. She did not report to work at Itundu Secondary School, prompting his colleagues to go look for her.
On March 7 Kimaiyo was found dead in her house located within the teachers' quarters. It was later reported that she was killed by her husband.
By then, Kosgei, who worked as a security guard in Murang'a town, had gone into hiding.
According to Mathira East Sub County Criminal Investigations Officer (SCIO) Wesley Kitienei, Kosgei's mobile phone was tracked in Mt Kenya Forest, not far from the school's location, which is at the foot of the forest.
At around 3pm, he changed location and activated his phone, and switched it off. He was later tracked in Thika on Sunday evening, a day before his body was found dangling from a tree in the Lavington area.
Neighbours who spoke to The Standard said the couple had a troubled marriage characterised by fights and quarrels, which had prompted their father-in-law to travel hundreds of kilometres away from Elgeyo Marakwet county to Itundu village in Nyeri county to reconcile the couple.
A day after the two agreed to resolve their marital issues following the intervention of their father's arrival, Kosgei made true his threat and killed his wife.
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"Rest in peace, my dear wife! I loved you. We promised each other so many things that we were yet to actualise, but I didn't know that I was alone in those plans because you had other plans with other men. All our problems started when you started bringing men to our marriage," read one of Kosgei's posts on X.
In another message posted on the day Kimaiyo was killed, Kosgei said, "I'm NOT okay, guys! I am mentally disturbed." The couple has left behind a daughter who was in Pre-Primary 2. Both Kimaiyo and Kosgei hail from Elgeyo Marakwet.
Paid for it
The woman was employed a few months ago as a Board of Management (BOM) teacher at Itundu Secondary School, where she taught science subjects.
In one of his posts on his X account, Kosgei claimed to have sponsored his wife's education and paid for her Teachers Service Commission (TSC) registration.
"I used to work at night as a night guard, during the day I take care of the kid as she goes to school," said Kosgei, claiming that his wife had been disowned by her family after she got pregnant with his child.
"Over the years since we started this relationship shenanigan, I have sold my property, including felling down my trees and selling my sheep, just to support her in school because immediately she got pregnant that was in September 2018, her dad disowned her," reads another post.
He added: "We agreed to be husband and wife since we had a kid together. We lived a smooth life without problems until this January when I got a certain job."
Kosgei also publicised screenshots of private messages between him and his wife and those of the wife and the alleged lover.
The body of Kimaiyo has since been transferred from Karatina Hospital Mortuary to Elgeyo Marakwet ahead of the burial scheduled later this week.
But even before the burial of the woman, Kosgei's family took a cow to his in-laws as a sign of remorse for the murder of their kin in line with Kalenjin traditions.
It is also a gesture to open windows for talks and also to halt any plan for revenge.