Detectives have taken fingerprints from the car suspected to have been used to ferry the kidnappers of slain Rongo University student Sharon Otieno and Nation journalist Barrack Oduor.
The police later drove the car from Oyugis Police Station to Nairobi for further forensic analysis.
Sources said the findings would add to a pool of evidence already collected to aid in nailing the people who killed Ms Otieno and her unborn baby.
"We are not leaving anything to chance and, in forensics, anyone mentioned in this case is a person of interest," a source conversant with the investigation said.
After dusting the black Toyota Fielder car, the detectives in a fleet of about 10 vehicles left for Nairobi with the ill-fated vehicle being driven by one of them.
Though the sleuths were reluctant to divulge any information, sources indicated that they were closing in on the main suspect who planned, financed and oversaw Sharon's gruesome murder.
"This informs the decision of the detectives to move to Nairobi. A key suspect will soon be arrested," the source revealed.
Police have linked the vehicle to Mr Caspal Obiero, a clerk at Migori County, who often runs errands for Migori Governor Okoth Obado.
On Wednesday, a court in Kisii allowed police to detain Mr Obiero for 10 days. He had surrendered to the police in Oyugis after the car registered in the name of his wife, Ms Olivia Oloo, was linked to the kidnapping and murder.
Ms Oloo on Sunday recorded a statement with the police, but detectives let her go after she proved that her husband was the one who had been using the Toyota Fielder at the time the murder happened.
Police also secured a 10-day detention of Mr Elvis Okoth Omondi, a policeman assigned to guard Mr Obado.
Mr Okoth had accompanied Mr Obiero to Oyugis Police Station but ended up being arrested.
Initially, police sources told the Nation he was arrested and disarmed because he had caused a commotion at the police station.
But his appearance in court may mean that the police are now linking him to the murder as well.
The vehicle was impounded on Monday and Mr Jack Ogombe, who is a taxi driver in Migori, arrested.
He is said to have driven the dark car mentioned in a witness account filed by Mr Oduor, who claimed he escaped the captors by jumping out of a moving vehicle.
On Monday, the suspect was produced at the Oyugis Law Courts where the magistrate allowed the police to detain him for two more weeks.
Mr Obado had been interrogated by detectives at the CID headquarters in Kisumu Town. Also, DNA results confirmed that the baby boy ripped from Sharon's womb was Obado's, thus putting the Migori governor at the heart of investigations.
Detectives say the governor's wife, Hellen, is also a person of interest, after suspects named her associates in the horrendous scheme.
On Wednesday, police postponed her scheduled interrogation at the Directorate of Criminal Investigations (DCI) headquarters as investigators gathered more evidence from suspects already in custody.
Also in custody is former Kanyadoto MCA Lawrence Mula and Mr Michael Oyamo, a personal assistant to Mr Obado.
A Kisii court last week detained the ex-MCA for 14 days to give detectives more time to investigate his possible involvement in the abduction and killing of the Rongo University student.
The High Court last week allowed police to detain Mr Oyamo, Mr Obado's aide, for 14 days at Muthaiga Police Station, Nairobi.