Muhuri has challenged police reports that the women were suicide bombers on a mission to blow up the station.
“When the story broke, the police narration of what really happened was contradictory from one source to the other," said Muslims for Human Rights chairperson Khelef Khalifa.
"At the moment they (police) have refused to state facts on what really unfolded."
Three terrorists killed in foiled attack at Mombasa Central police station
Three more arrested after Mombasa Central police station terror attack
Two of the women were identified as Fatuma Omar and Tasnim Yakub, who is believed to have been the leader. The third woman is yet to be identified.
Police termed them terror suspects saying they pretended to report phone theft but hurled a petrol bomb at the station, forcing them to open fire in self defence.
This was said in an announcement by government spokesman Eric Kiraithe on Tuesday.
Amid growing concern about extrajudicial killings by organisations including Human Rights Watch, Muhuri said the shootings were a continuation of the crime.
“We hold that what police said is a total lie and we cannot let it go unchallenged. They are cooking up stories to cover up the whole incident,” said Khalifa.
He said the group will sue the station's OCS and officers seen in the video of the killings.
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Muhuri said the "girls" - two sisters and a friend who finished form four last year - were mishandled when they went to report the crime.
The lobby said a witness reported that when they got into the station, the officer on duty wanted to tear off the burqa one of them was wearing, forcing a reaction.
Khalifa said it was during the commotion that followed that the woman stabbed the officer with a key chain, but that the policeman insisted on "undressing" her.
He said other officers then opened fire and killed all three women, and accused them of dousing the bodies in kerosene and setting them ablaze to conceal the killings.
A clip seen by the Star shows one of the women with her hands in the air in surrender, and a policeman walking towards her while shooting.
“We question why even after surrendering the police continued firing at the lady," said Khalifa.
"We suspect the bodies were doused in kerosene and set ablaze to make it seem they had bombs, because if it is true they had a petrol bomb that they threw into the police station, why didn't we have any injuries? And if there were, where are the victims?"
Police are yet to show the knife and the suicide jacket they said they recovered from the body of one of the suspects.
“The word 'terrorists' invokes fear. When police want to justify any action of extrajudicial killing they brand the victims terror suspects because the public buys such narratives without question.” Khalifa said.
He further claimed the arrest of Haniya Saggar, who is Aboud Rogo's widow, in connection with the attack, was part of the conspiracy theory by police.
Police said Saggar is suspected to have financed the three women as there was proof of a transaction between her and one of them.
But Muhuri said: “It is a case of pure framing and efforts by police to build a case to cover up their action."
"As a matter of fact we have established that on the fateful day the telephone line of one of the girls had been used to send Sh10,000 to Haniya, which she sent back because, as usual, if you get money from someone you don't know you send it back. Those girls were not known to her."
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Khalifa said urgent post mortem examinations need to be carried out on the bodies, and thorough investigations done by the Independent Policing Oversight Authority, with a view to punishing those culpable.
Read more: http://www.the-star.co.ke/news/2016/09/20/video-cops-accused-of-killing-three-innocent-girls-at-mombasa-central_c1423846