Jason Nelson, 32, admits killing Jordan Maguire, 20, at his Luton home, in a "spree of violence" on 26 May 2013 but claims it was done in self-defence.
The former resident of Marsh Farm Estate in Luton has pleaded not guilty to murder, rape and sexual assault.
A man who saw Mr Maguire stabbed three times said the accused "showed no regrets or remorse" afterwards.
Luton Crown Court heard the attacks happened at Mr Maguire's home in Thrales Close between 18:00 and 20:15.
The prosecution allege Mr Nelson was in the middle of a spree of violence, having sexually assaulted a 25-year-old woman in the stairway of some flats and then a 60-year-old woman in her flat.
Witness Dennis Kamau said he and his girlfriend were looking to buy some cannabis when he came across Mr Nelson near the Nisa store on the estate.
He took the pair to Mr Maguire's home where the men entered the house while the woman stayed outside.
After the pair agreed to share a deal, they went to the kitchen where Mr Maguire removed a tin from a kitchen cabinet.
Mr Kamau said: "The next thing I saw was a knife rise above and attack Jordan.
"I saw the knife go into Jordan. Jordan acted all shocked. He stabbed him a second time."
Mr Kamau told the jury the victim was then stabbed in the back by Mr Nelson who said "You little pussy" before putting the knife away and riding off on his bike.
"I was scared, terrified and shocked," said Mr Kamau.
Asked how the accused appeared, he said: "He showed no regrets or remorse."
A stab wound to the chest had punctured Mr Maguire's aorta and he was fatally injured.
The jury earlier heard Mr Nelson stayed for two weeks with a girlfriend in Ipswich before flying to his native Grenada and was later arrested in Trinidad.

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22 September 2015 Last updated at 16:42 BST
The pupils, from Sussex, have designed and built their own high-tech vehicle and will now compete in the three thousand kilometre race.
Only solar-powered cars are allowed in the competition, which involves the teams driving from Darwin to Adelaide.
Watch Hayley's report to see how the team are preparing.

The woman, in her early 20s, was rescued by RNLI lifeguards who were on duty for the first day of the season at Newquay's Fistral beach.
Lewis Timson, lifeguard supervisor, said the surfer's longboard leash snapped while she was competing in the Natty Surf Jam one-day event.
He described conditions at sea as "pretty wild".
The "distressed" woman, who is thought to be from Newquay, was taken ashore, but was not believed to need hospital treatment.
The festival was arranged in memory of 25-year-old local surfer Nathaniel Loney who died after battling severe depression and bi-polar disorder.
The money raised is being given to the Invictus Trust, a charity which supports young people with mental health issues.
The rescue highlights statistics from the RNLI, which show a big increase in the number of incidents around the South West.
Last year, beach lifeguards dealt with more than 11,000 incidents, while lifeboat crews launched 1,614 times - a 35% increase from the previous year.
There will be full-time lifeguard cover at Fistral and Croyde in Devon until the end of the season, with a number of other beaches in Devon and Cornwall patrolled during the Easter school holiday period.

8 August 2016 Last updated at 10:28 BST
A man who stabbed a drug dealer to death showed no remorse after the knife went in, a jury has heard.
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A group of school students will be the first team from Europe to take part in a big solar powered car race in Australia.
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A woman has been rescued from the sea after getting into difficulty during a charity surfing festival in Cornwall.
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The BBC's Dave Lee reports from the Def Con hacking conference in Las Vegas, where Hillary Clinton has gained some unlikely support from the hacking community.