Justice Joel Ngugi also convicted Muthoni’s co-accused Isaac Isaac Ng’ang’a alias Gikuyu.
The convictswill be sentenced on May 18.
During the trial, Muthoni who has been in remand for nearly five years following the murder, defended herself against the charge of killing Mbuthi and said it was his fellow who orchestrated her husband’s death after he refused to play into their game over transfers.
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The court heard that the principals, who influenced transfers and promotions of teachers in the region, were aggrieved after Mbuthi was posted to the school while she was promoted to head Icaciri Secondary School without going through them.
Muthoni claimed that the cartel had demanded Sh1 million from them to facilitate their transfer to schools of their choice.
She further claimed that the cartel framed her after murdering her husband.
Muthoni was charged alongside Ng’ang’awith the murder of Mbuthi between November 4 and 11, 2016 in Kiambu County.
According to the prosecution, Ms Muthoni hired four people to eliminate her husband after she suspected him of having extra-marital affairs.
One suspect, Joseph Kariuki, was sentenced to seven years in prison for manslaughter after he confessed to taking part in the murder.
The fourth suspect, Nelson Njiru, is still at large and efforts to trace him have been fruitless.