Former Sports Cabinet Secretary Rashid Echesa, who was arrested on Friday after he was captured on video assaulting an official of the Independent Electoral and Boundaries Commission (IEBC) in Matungu, has been transferred to DCI headquarters in Nairobi.
Mr Echesa, who is a close ally of Deputy President William Ruto, was arrested when he presented himself to police in Mumias after he had been declared armed and dangerous.
He spent the night at the Kakamega police station before he was picked by a team of officers who drove with him to Nairobi early Saturday.
Western region police commander Peris Kimani confirmed Mr Echesa was transferred to DCI offices in Nairobi but declined to give further details.
"There are investigations being conducted by the DCI and that's why he is being transferred there. This matter is being handled by the DCI," said Mrs Kimani.
The assault on the electoral agency official took place on Thursday as voting got underway at the Bulonga Primary School polling station.
The by-election in Matungu was marred by violence and incidents of wide spread voter bribery.
Mr Echesa is accused of slapping an IEBC official during an altercation which erupted over UDA poll agents who had been ejected from the polling centre.
He later went into hiding after the video went viral social media. On Thursday, police officers raided Mr Echesa's home at Shibale in Mumias West constituency did not find him.
His arrest came after police asked him to surrender to the nearest police station.
The IEBC chairman Wafula Chebukati had asked police to arrest Echesa and he was prosecuted.
ODM Secretary General Edwin Sifuna had called on police to ensure all suspected who took part in acts of violence during the by election were prosecuted.
"We shall be setting a bad precedence if the perpetrators of violence acts in Matungu will go scot-free. Action has to be taken against them," said Mr Sifuna.
The body guard of Kakamega Senator Cleophas Malala was arrested after he shot at a group of youths, injuring a resident at Munami polling station.
The administration police constable was disarmed and arrested along with six other people who stormed the polling station and disrupted voting, claiming IEBC officials were watching as ODM agents were stuffing ballot boxes without stopping the malpractice.
The administration police constable and the six suspects will appear in court on Monday.