A 64-year-old man died after he and his wife were tied up with tape and threatened with a gun during a burglary at their bungalow.
Scotland Yard said burglars entered the home of Edward and Anne Syrad in south east London last night.
A relative, who did not want to be named, said Mrs Syrad found her motionless husband - known as Ted - after managing to free herself.
He said: "The burglars walked into the bedroom and she was held at gunpoint. It's unclear what happened to Ted.
"As far as I'm aware she was tied up in one room and Ted was in another room. He was a crafty smoker, so it's thought he was in the garden having his last cigarette of the day and they came over the wall.
"She rang 999 after the burglars left. She'd managed to hop into another room where she saw Ted. She tried to nudge him but he wasn't moving."
A post-mortem examination is due to take place tomorrow morning and no arrests have been made.
Floral tributes were left at the couple's home on Edendale Road, Barnehurst, where they are thought to have lived for several years.
The man said he did not believe it was a random attack as his relatives are "quite well off".
"I don't think it was on the off chance," he said, after laying flowers. "From the whole street, to be targeted - the house is nothing special. There's nothing different about them. I think someone knew what they were doing."
Mrs Syrad runs a building and property company in Greenwich, south east London, and had been due to retire later this year, after 40 years in the business. Her husband did not work due to poor eyesight.
"That's the gutting thing," the relative added. "They had 10 months before enjoying the rest of their lives together."
He said Mrs Syrad's stepson, Colin Philby, who is due to get married in Wales in two months' time, called Mr Syrad "Dad".
Mr Syrad had two children of his own, Paul and Julie.
The relative described him as a "fantastic" man who enjoyed a party. He was a Millwall fan who went to his local Wetherspoons pub twice a week with his wife, he added.
Mr Syrad's family are devastated, the relative said, and are being supported by Mrs Syrad.
"The kids are finding it hard," he said. "She's being their rock. I can't imagine how she is. It's just unthinkable."
One of the floral tributes read: "Dear Dad, I can't believe that someone can take your life from us.
"I love you with all my heart and can't believe you're gone. I can't tell you how much I'm going to miss you. Love, your son Colin."
Another, attached to a single red rose, read: "Dear Grandad, I will miss you forever."
One, addressed to "Grandad Ted", said: "I love you so much."
Another bunch of yellow roses bore the message: "To Dad. Words can't describe how lost we are all going to be without our rock."
Neighbours said they were shocked to hear what had happened to the "pleasant" couple.
Stuart Aldridge, 33, whose garden backs on to that of the bungalow, said: "They're a pleasant couple and would kick the kids' balls back over the fence.
"All I understand is that it was a burglary gone wrong. Why they were targeted. I don't know.
"I think people are scared by this. I've got three kids - they were alone in their beds and this was going on literally in the back garden."
Mr Aldridge said he believed the burglars had been armed, but Scotland Yard said it could not confirm that.
Emergency services were called at about 10.25pm last night and Mr Syrad was pronounced dead at the scene.
Detective Chief Inspector Cliff Lyons said: "One line of inquiry is burglary, although at this early stage of the investigation we are keeping an open mind with regards to a motive.
"We would appeal for anyone who may have seen or heard anything, or has any information regarding this murder, to come forward and assist police."