The Independent Policing Oversight Authority (IPOA) has launched investigations into the death of Mombasa tout who died at Changamwe police station on Tuesday.
Caleb Espino Otieno,40, was arrested on Monday evening by three officers at Mikindani while enjoying a drink at White Castle bar.
He was however found murdered on Tuesday.
The suspect was nabbed alongside a friend Enos Alubisi and a woman vendor.
Muslims for Human Rights has accused police of trying to cover-up the death.
MUHURI rapid response officer Francis Auma said they will provide an independent pathologist to eliminate foul play in the murder.
"Killings in the hands of police has become too much. IPOA is overwhelmed," Auma said at Mombasa High Court.
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MUHURI chairman Khelef Khalifa said police inquiry must be launched to unravel the truth.
"Police must take action against the offender," he said
IPOA has already recorded statements from police officers who were on duty.
Otieno is survived by six children.
His first-born, Nelson Otieno, said the father who hails from Luanda in Western Kenya, has been working at a tout for five years.
"My dad didn't have to die this way," the son said in sobs.
Nelson said his father was calm even after drinking.
A neighbour, Jennifer Mutua, said Otieno was caring and understanding.
It is alleged that the deceased was pushed and hit by a metal bar along the cell's corridor.
He died instantly. His body was moved to Coast Provincial General Hospital morgue.
His death occurred around 12 am on Tuesday, just a few minutes after he was booked.
Alubisi and the vendor are due to be charged at Mombasa High Court.
Changamwe OCPD Peter Omwana said he will address the media on Thursday afternoon.