Isinya Sub-County Directorate of Criminal Investigations (DCI) boss Benjamin Ndubai on Wednesday told The Standard that the assaulted KPLC engineer had filed a report at their station.
He said apart from the assault, the MP also faces investigations over the misuse of his firearm as he was filmed attempting to reach for his gun.
The incident provoked Kenya Power workers in Kitengela town to organize a peaceful demonstration.
Waving twigs and placards, the more than a hundred employees walked from their offices to the Kitengela Police Station where they demanded justice for their colleague.
"We want justice to be done without compromise. Eng Onkangi must get justice,'' said Musa Matanono, an employee of Kenya Power.