Detective Superintendent Shaun Edwards said Adris Mohammed "must have known" David Varlow would die after the burglar tied him up at the victim's home in Halesowen last year.
Mohammed was found guilty of Mr Varlow's murder on Wednesday.
It was the second time the 44-year-old had targeted the pensioner, with an unsuccessful break-in attempt taking place on October 24 when Mr Varlow scared the defendant off.
However, just over a week later and Mohammed returned in the early hours of November 3 and police believe the intruder had expected his victim to be asleep – which he wasn't.
Instead it marked a "horrendous" series of events where the vulnerable pensioner, who was not in the best of health, was threatened with a knife in his own home and tied to a chair.
Det Supt Edwards, head of homicide at West Midlands Police, said Mohammed tied Mr Varlow up using things from around the house including cable ties, belts and a phone line which he cut to leave his victim helpless.
"We think he expected Mr Varlow to be asleep and Mr Varlow was awake and that's why Mohammed attacked him," said Det Supt Edwards.
"He tied him to a chair using cable ties and other things found in a house and we know he threatened him with a knife and attacked him to get his pin number for a bank card which he subsequently stole.
"And Mohammed cut the phone lines so Mr Varlow, tied to a chair and vulnerable, was unable to call for help – and was simply left to die."
While his victim was tied to a chair, the defendant alongside three others – including co-defendant O’Shay Swan and two others already convicted – went on a nine-day spending spree, using the card in over 350 occasions to steal more than £8,000 from Mr Varlow's account.
On November 12, the defendant returned to his victim's home on Manor Lane in Halesowen and it is believed he returned to steal some more items. A post-mortem showed Mr Varlow, in all probability, was dead when the callous burglar returned.
"We know he untied (Mr Varlow) but rather than call for help, or call the police, he just left him. He simply left him there and Mr Varlow was not found until a few days afterwards when concerned neighbours called the police," the senior detective said.
It is believed Mohammed acted out of greed, had no thought for Mr Varlow and had displayed a "lack of humanity" in tying his victim up – safe in the knowledge the pensioner could not call for help, with the phone line being severed, while he and others spent his money unhindered.
Mr Varlow had been dead for some time before he was examined by a pathologist and it is believed he had suffered a "stress-induced" heart attack after his ankles and wrists were bound, jurors heard.
Birmingham Crown Court heard during the trial that Mohammed, of Icknield Port Road in Birmingham, was a prolific burglar and had numerous convictions for the crime. It was this which helped bolster the prosecution's case, alongside painstaking forensic and CCTV investigations which led to his swift identification and arrest, and subsequent conviction.
Det Supt Edwards said forensic examination of the scene could prove the callous burglar was there, and hundreds of hours of CCTV could prove his whereabouts before and after the break-in.
The group of four accomplices used cash points and bought some jewellery during their spree, with a bangle subsequently pawned to get money – essentially laundering the money – as Mohammed passed the card around.
Mr Varlow lived a "very simple life" and used to speak to his family, who live up in the North East, regularly on the phone, keeping himself to himself. But he was very sociable to his neighbours, often speaking to them when he was out in his garden, and was the main factor in them raising the alarm after not seeing him for a while.
The senior detective said the original attempted burglary, on October 24, was investigated initially and there was no line of enquiry. However, a police officer visited Mr Varlow – which the family were grateful for – and offered him advice in case the burglar returned.
Det Supt Edwards said: "Mr Varlow was 78, he was vulnerable and he was tied to a chair. Mohammed must have known that he was putting his life in danger and so much so he cut the phone lines, so Mr Varlow could just not call for help – that is just callousness to the highest degree.
"He cut the phone lines intentionally. And he [Mr Varlow] wasn't able to look after himself by going and having a drink or having something to eat. The one intention for Mohammed then was for Mr Varlow to die so Mohammed could use that card unhindered.
"He tied him up using things around the house, belts, cable ties and the phone line he had cut as well. Mohammed made no comment [in the interview], he refused to answer any questions and did not give an account of what happened."
Det Supt Edwards said Mohammed still hadn't taken responsibility for his crimes – having tried to mitigate his role in Mr Varlow's murder – during the trial, adding: "He showed absolutely no remorse."
Mohammed, 44, from Icknield Port Road in Birmingham, was charged with attempted burglary at Mr Varlow's home on October 24, aggravated burglary on November 3, murder and fraud. He was charged with a further burglary on November 12 and denied all charges.
O’Shay Swan, 42, of Winson Green Road, Birmingham, was accused of burgling Mr Varlow’s home on a day between November 10 and 13 and fraud in relation to the use of a bank card on November 12.