Police have said that a missing car key may lead to the killer of Dr Victoria Anyetei, stabbed to death outside her home in Dartford 16 days ago.
The 54-year-old consultant paediatrician's body was discovered by her son in her car on the driveway of their home in Teynham Road at around 10.30am.
She had been killed as she set off for work at St Thomas's Hospital in London.
Police have appealed to neighbours to search their gardens for her missing car key - and the murder weapon.
Today her bother, Dr Jonathan Anyetei, begged for information.
"We would like to appeal directly to people in the community and say please, please come forward if you have any information about my sister's murder."
And he added: "It's a cowardly thing to attack an innocent woman on her way to work. It's a cowardly act."
Dr Victoria Anyetei died outside her home in the quiet cul-de-sac where she had lived for eight years on August 14.
Detective Chief Inspector Anne Brittain of Kent Police said she believed Dr Anyetei was attacked as she got in her silver Toyota Avensis to drive to the railway station and catch the train to work.
Police enquiries are focusing on finding the missing car key and the knife used to kill her.
DCI Brittain said: "Her killer is believed to have taken this key away after having murdered her and I'm sure someone out there can help us to find this key.
"It could lead us to the murderer.
"It is very likely that the killer threw this key away after having left the scene."
The missing key was attached to a keyring on a leather fob with a metal Toyota insert. A small silver key may also have been attached to the keyring.
DCI Brittain said: "Did you see anyone with a similar type of key and wondered why they are in possession of it? If you have information linked to this it is important that you come forward and talk to us immediately."
She added: "We're still looking for the knife used by the killer. I would appeal to anyone in the area to re-check their gardens. We still have not found the murder weapon."
Dr Jonathan Anyetei, 61, a dental surgeon, of Stevenage in Hertfordshire, said his sister was a "dedicated mother and loving sister".
He said: "She was the glue for the family, she held us all together and she was also a safety net in the sense that if any of us were going to fall, she would be there to support us."
Dr Jonathan Anyetei revealed he last spoke to his sister, a devout Christian, on the telephone about two weeks before her death.
He said: "She seemed all right. Most times she spoke to me about her problems but last time she was talking about her son and how she was happy he was going to university to study law."
He also revealed they were jointly planning a holiday to visit their brother in South Africa. His sister had also recently returned from a trip home to their native Ghana.
DCI Brittain said a dedicated team of 20 officers were making enquiries at her workplace and church and with friends and family.
She said: "This attack doesn't make sense. There's no clear motive, there's no obvious evidence, it's a very complex case and it takes time to investigate."
DCI Brittain also said: "She was a professional lady who was involved very heavily with her family and an avid churchgoer."
Police continue to pursue "many avenues", including the possibility Dr Victoria Anyetei was murdered by a disgruntled former patient.
DCI Brittain said there was no evidence to suggest the attack was racially motivated.
She said: "We must emphasise we still want people to come forward and help us build up a more detailed picture of what was going on in the area in the morning Victoria was killed.
"I'm disappointed we haven't got more witnesses who did see something that day."