Annie Besala Ekofo, 53, and Bervil Kalikaka-Ekofo, 21, were found dead in East Finchley on Thursday.
Scotland Yard said officers will explore whether anyone else linked to their address could have been a target.
It comes as their family released tributes to the pair.
Police were called to the flat in Elmshurst Crescent by the London Ambulance Service early on Thursday morning.
Four other people, including a child, were also at the property at the time of the incident but were not harmed.
Officers said they were keeping an open mind as to a motive for the shooting.
Launching a fresh appeal for witnesses, Det Ch Insp Andrew Partridge said: "We have already spoken to a number of people who have come forward and provided useful information.
"Whilst the murders took place early in the morning, I am confident that there would have been people up and about, getting ready for work and school.
"It is possible that someone may have noticed a stranger on the estate, or a vehicle that is not usually there."
He said specially trained detectives were providing support to the "devastated" family.
Mr Kalikaka-Ekofo, who was studying psychology at the University of West London, was described by his mother Maymie Botamba Chantelle as a "bright, intelligent young man... always caring for those around him".
"He was always making people laugh," she said.
"He was very creative and was in love with music, photography and art."
His father, Patrick Ekofo, said his son "never looked for trouble. He was always the peaceful one".
Mrs Besala was described by her family as a "wonderful and loving mother and wife, always smiling... a glue that kept everyone together".

Cardiff narrowly missed out on the Championship play-offs last term, finishing eighth in the table.
But under new head coach Paul Trollope, Pilkington thinks the Welsh side are capable of better.
"We fell just short [last season] and we were all really disappointed with that. We felt we had the squad to get in the play-offs definitely," he said.
"It's going to be a tough season again, just like it was last year, but hopefully we can be right up there come the end of the season."
Pilkington, 28, scored Cardiff's first goal in their 4-0 friendly win at Shrewsbury on Saturday.
The Republic of Ireland international played in attack, having moved from the wing to a central forward role last season.
Pilkington made the transition under former Cardiff boss Russell Slade, who was replaced by Trollope in May.
Trollope had been working under Slade before then, and Pilkington believes that smooth transition has helped the Bluebirds in their preparations for the new campaign.
"The gaffer was working with us last season so we know how he works," he added.
"We know what he's about and we know we have to be on our toes all the time.
"He's come in and changed a few things. It's been good up to now so hopefully we can carry on working really well."
Detectives investigating the killing of a mother-of-nine and her nephew in a shooting at their north London flat say they have not found any evidence to suggest they were the intended victims.
[NEXT_CONCEPT]
Cardiff City forward Anthony Pilkington believes the Bluebirds can challenge for promotion this season.