Police officers risk losing their jobs and pensions if they fail to properly investigate domestic abuse including stalking, harassment and coercive control following a landmark misconduct ruling.

Sergeant Sidney Rogers, PC Adrian Brown and PC Christopher Moore – all from the Metropolitan police – were found guilty of gross misconduct earlier this month for their handling of events in the days before the killing of Linah Keza, 29, by her former partner. Each officer has received a final written warning and any further misconduct will result in dismissal.

David Gikawa, 38, stabbed Keza to death in her east London home in front of their two-year-old daughter in 2013. He was convicted of murder and jailed for life. The prosecution said during his trial that the “systems in place” failed to prevent the death of Keza, who had been in frequent contact with police.

The inquiry into the officers’ actions followed an investigation by the Independent Office for Police Conduct. Gross misconduct findings against the police are rare. The inquiry panel heard that Rogers, Brown and Moore failed to properly assess the risk to Keza. Gikawa, who had been told that he could only go to Keza’s flat accompanied by officers, was later allowed to go to her home without a police escort.

Keza, a former model who hoped to become a social worker, came to Britain from Rwanda in 2007. She met Gikawa in 2009 and endured four years of physical, emotional and psychological abuse before her death.

Keza’s family were disappointed the officers have not been sacked. Susan Asiimwe, a lawyer in Kigale and Keza’s sister, who has adopted Linah’s daughter, said: “We blame no one but David Gikawa for taking Linah’s life. But Linah trusted the police and they let her down.

“Although we are disappointed that no officer will lose his job, after six years of fighting we are grateful that there has been some individual accountability for the failure to protect her. We hope that Linah’s case can be used as an example for change and learning so that something positive can come out of our terrible loss.”

Commander Catherine Roper, of the force’s directorate of professional standards, said: “We always look to learn from our mistakes made during investigations. We are continually working to improve our response to domestic abuse in all its forms.

“We always expect the very highest standards of conduct and behaviour from our officers … when officers fall short of those standards, they can expect to be held to account.”

Sophie Naftalin, solicitor for the family, said: “The Metropolitan police service has accepted that there were serious failings in Linah’s case and that lessons will be learned.

“For these assurances to be meaningful they need to invest in the resources and training to ensure that officers on the ground understand how to assess risk and investigate the criminal offences in domestic abuse cases, such as harassment, stalking and coercive control.”