A horrified shopworker described the harrowing moment she heard a teenage victim utter his last words.

Malcolm Mide-Madariola, 17, was fatally stabbed outside Clapham South tube station on Friday, November 2. He was the second teenager to be knifed to death in south London in the space of 24 hours and the 21st teenager to be murdered in the capital this year.

SEE MORE: Teenager dies from stab wounds outside Clapham South Tube Station

The woman saw him clutch his stomach after he was stabbed in the chest and heard him cry "oh no" before falling to the pavement as his attacker walked off.

She said she was waiting at traffic lights when she witnessed the attack after finishing her shift and grabbing a few groceries on her way home.

SEE MORE: Clapham murder victim named

The woman, who asked not to be named, sobbed as she said: "I heard his last words. He said 'oh no' holding his stomach, and then he just fell onto the pavement.

"I didn't hear him scream. He looked so helpless. I was waiting at the lights with two elderly ladies when I saw the two boys arguing. One boy pushed the other one before he produced the knife.

SEE MORE: Clapham South Tube station: Community in shock after stabbing

"It was a long knife, much bigger than a normal kitchen knife. Then I just saw the young boy standing there after he was stabbed and the other one walking away and looking back.

"To know I heard his last words was so horrible. They were both black and wearing normal clothes, not school uniforms, but I cannot describe them any more than that."

Detectives investigating Malcolm’s murder believe it may have been linked to an earlier scuffle.

SEE MORE: Tributes paid to teenager who was fatally stabbed in Clapham

Police say college student Malcolm, who lived in Peckham, may have been attacked as a result of an earlier altercation between two groups of youths just yards from where he was knifed.

Police are continuing to investigate the murder as well as the killing of 15-year-old Jay Hughes, also known as Jai Sewell, 24 hours earlier seven miles away in Bellingham.

Detectives don't believe the two cases are linked and no arrests have been made in either investigation.