Raila wants student's killers quickly brought to book.
Ms Otieno's body was found in K'odera forest in Oyugis, Homa bay county, on Wednesday.
Rongo MP Paul Abuor also said the probe should be fast-tracked "and those behind the act prosecuted regardless of who they are and the positions they hold".
Opposition leader Raila Odinga wants the criminal investigations agency to speedily investigate the brutal murder of pregnant university student Sharon Otieno.
Ms Otieno's body was found in K'odera forest in Oyugis, Homa Bay County, on Wednesday.
The second year student of Rongo University had been kidnapped alongside the Nation's reporter Barrack Oduor on Monday.
Mr Oduor narrowly escaped death by jumping out of a speeding vehicle in which the two of them were.
Speaking during a funds drive for Migori senator aspirant Ochillo Ayacko's campaigns on Wednesday evening, Mr Odinga asked the Director of Criminal Investigations to quickly unravel the murder and identify Ms Otieno's killers.
"I condemn in the strongest terms the brutal murder [Ms Otieno]. I call upon the DCI to investigate the matter with speed and bring to book the perpetrators of this heinous act," he said.
"It is very unfortunate that a young girl, who was pregnant, was murdered. My condolences to her family."
At the same event, Rongo MP Paul Abuor also said the probe should be fast-tracked "and those behind the act prosecuted regardless of who they are and the positions they hold in the society".
Government spokesperson Eric Kiraithe has assured the country that the incident will be investigated expeditiously.
"I take this opportunity to assure the public and media fraternity in particular that this matter will be expeditiously investigated and that perpetrators of this heinous crime will face the full force of the law," Mr Kiraithe said in a statement.
DCI George Kinoti has dispatched a team of detectives to Migori and Homa Bay counties to get to the bottom of the murder.
Mr Kinoti has promised to zero in on the perpetrators of the crime in a record three days.
Meanwhile, the office of Migori Governor Okoth Obado has denied that he was linked to the abduction of Mr Oduor and Ms Otieno.
County communications boss Nicholas Anyuor claimed the allegations are meant to ruin Mr Obado's reputation.
"The reports linking [Ms Otieno] to Governor Obado are malicious and unsubstantiated. The media should stop using the name of the Governor in reporting the incident," he said.
Mr Obado's personal assistant, Mr Michael Oyamo, was arrested on Tuesday after he was linked to the abduction of the two.
Rongo University students took to the streets on Wednesday, demanding an explanation from the Migori government. They said they will demonstrate until Mr Obado addresses the matter.