"I believe I have what it takes to represent your interests in the Senate. I tried in 2017 to run for the top job but you all know what happened. I am now determined to serve you in a different capacity. Please walk with us,” Mr Ayacko told residents of Kuria.
ODM leader Raila Odinga is expected in the county at the tail end of the campaigns to rally support for Mr Ayacko.
Mr Ayacko is considered the front-runner after Mr Otieno withdrew from the race.
since last week when incident occurred.
The ODM camp has been accused of using the case to disparage Mr Obado hoping to capitalise on the moral perception crisis that he is currently facing in a bid to neutralise his influence in the race.
"We know some people have taken advantage of Sharon's case to pin down the governor for political expediency. We reject this political opportunism," Mr George Olumwa Kidikibudi, a political activist, said.
He added: "We call upon the aspirants in the upcoming by-election to stop politicising Ms Otieno's murder and if they continue with what we are seeing, we shall be forced to come in."
A source close to Mr Oketch told Nation that his camp has been dealt a big blow by Ms Otieno's murder.
"It's true the incident is a major setback to our campaigns because Mr Obado will now concentrate on clearing his name and it's also true he has lost some moral ground," an ally of Mr Oketch, who asked to remain anonymous, said.
"We were really banking on his massive grassroots networks and of course his deep pockets," he added.
The seat fell vacant following the death of Mr Ben Oluoch Okello who succumbed to the throat cancer at a Nairobi hospital.
Apart from Sharon's murder, the Kuria community is likely to play a role in who will win the seat.
The region, which has close to 87,000 votes, supports Jubilee Party. However, given that Jubilee has not fielded a candidate, the region's votes are open to any candidate who manages to convince the residents.
Though Mr Solomon Hodo of People's Democratic Party hails from Kuria West, his Luhyia ancestry has denied him an outright command of the region's votes.
Other candidates for the seat include businessman Mr Jobando Peter (Green Congress Party of Kenya), Mr Ogolla Dickson Ogolla (Independent) and Mr Otieno Samwel Otieno (Independent).