Maria Stubbings, 50, was strangled by Marc Chivers at her home in Chelmsford, Essex, in 2008.
Earlier this year, an inquest ruled she was failed by Essex Police.
Ms Stubbing's son, Bengi, who was 15 when she was killed, said he wanted a public inquiry to "spark more awareness around domestic violence".
A petition set up by domestic violence charity Refuge and the families of victims, including Ms Stubbings, has been signed by almost 50,000 people.
It is calling for a public inquiry into why victims of domestic violence are not getting protection.
Bengi Stubbings said he wanted the issue to be "more in the open".
"I'd like it [the inquiry] to get agencies to connect and come together to protect the public," he told BBC Look East.
In October, the jury at an inquest into Ms Stubbings' death said Essex Police had failed in almost every part of its investigation.
It said the force had made a catalogue of errors, starting in July 2008 when Ms Stubbings first contacted them after being assaulted by Chivers, who had served 15 years in prison in Germany for killing a former girlfriend.
Essex's chief constable, Stephen Kavanagh, admitted the force had failed to protect Ms Stubbings and her son, but said work was being done to make sure her death was not "in vain".
Mr Stubbings said he thought the "culture" around domestic violence "needed to change".
"In society, we're not as aware of what the signs are," he said.
"We all need to help each other to raise awareness about what domestic violence really is."
The family of a woman who was murdered by her ex-boyfriend - a convicted killer - are calling for a public inquiry into her death.