An inquest jury determined that police errors played a role in the deaths of Raneem Oudeh and her mother Khaola Saleem in Solihull in 2018.
The West Midlands Police Department has apologized to the family.
Zoe Billingham, Her Majesty’s Inspector of Constabulary, stated that officers “failed” them.
“In all steps, the victims in this particularly tragic and shocking case were failed and let down by the police,” she told BBC Radio 4’s Today programme.
She said it was “astonishing” police had invited Ms Oudeh’s estranged husband Janbaz Tarin for a voluntary interview and that officers “possibly didn’t take the victims seriously”.
Tarin admitted murdering the two women and was jailed for a minimum of 32 years in December 2018.
West Midlands Police had “so many opportunities to save their lives, right up until the end”, Mrs Saleem’s sister, Naur Norris, said after the inquest.
Ms Oudeh made six 911 calls in their final hours after Tarin hit her at a restaurant and followed them home, but officers were unable to reach them in time.
Ms Oudeh’s screams as she was attacked could be heard in the final call, which the inquest heard.
Ms Norris claimed that the police had “failed Khaola and Raneem beyond comprehension.”
Tarin’s actions had not been reported to police for the first time, with the Independent Office for Police Conduct (IOPC) detailing 10 domestic abuse incidents reported to West Midlands Police between April and August.
The IOPC found that the force failed to conduct adequate intelligence checks when responding to domestic incidents involving Ms Oudeh and Tarin and “treated each incident in isolation.”
The lack of time police officers have to do their job well has to be addressed by West Midlands Police, Ms Billingham said.
“One of the key lessons here for the force is to make sure that you free up police time so they can take domestic abuse seriously,” she added.
The force had made changes since the murders, including increasing the number of officers investigating domestic abuse offences, Assistant Chief Constable Andy Hill said.
But he accepted “none of this will undo the devastation that the murders of Raneem and Khaola caused to their family”.