James Owusu, 22, was gunned down in the doorway of his family home in north-west London on Wednesday evening.
His family said two men walked casually past the open front door and blasted him three times at close range in front of his mother, Deborah.
She tried in vain to stop the blood coming from wounds to her only son’s side and stomach but he was pronounced dead at the scene.
Mr Amiah, who runs a shipping firm in Wembley, told the Standard: “He’d been watching the Champions League match at home with his uncle, who was visiting from Ghana, and then went round to see his best friend next door.
“He came back around 10.30pm. He’d left the door slightly open and they put the gun around the door. He was shot three times and fell to the floor just inside his house
“His mother ran to him and said Qwasi ‘why has this happened? Have you done anything to anyone?’ He said: ‘Mum I haven’t done anything to anyone.. I don’t like trouble.”
“She did what she could to try to help him before the ambulance arrived. She was distraught, she felt helpless and hopeless. She was still clearly in shock when I saw her.
“None of us know why this has happened, it’s a complete mystery. He was a good boy, he worked hard and studied hard and wanted to be a success.
“I ‘ve known him since he was six years old and he was like family to me.
“He would talk to me about things. It seems impossible he had a double life we didn’t know about that someone would want to do this to him.”
Mr Owusu had hoped to study a masters in accountancy.
He worked at Mr Amiah’s firm, which couriers containers and packages to Ghana, and played African and Caribbean music at private parties and weddings under the name DJ Skillzy.
He was born in the UK and was the only child of his parents who moved from Ghana to the UK before his birth.
Detectives from the Homicide and Major Crime Command have launched a murder inquiry. No arrests have been made.
A Scotland Yard spokesman said: “Police were called by the London Ambulance Service at 10.45pm on Wednesday to reports of a shooting in Tynsdale Road.
“Local officers and firearms officers attended the location and found a man in his 20s with gunshot injuries. He was pronounced dead at the scene.”