Two teens accused of the "motiveless" murder of a 21-year-old student with a machine-gun appeared at the Old Bailey on Thursday.

Robel Tewelde, 21, died instantly when he was blasted in the heart at a block of flats in Clapham on October 2 last year.

Jermaine Callum, of Springfield Estate, Clapham and Ngozi Edwards, of Hemans Road, Nine Elms, both deny murder.

The court heard Robel was visiting friends the Studley Estate, Stockwell when Callum, the alleged gunman, and Edwards, the alleged back-up, both 18, arrived shortly before midnight.

Looking at CCTV footage prosecutor Nicholas Hilliard QC said: "Callum can be seen to be opening the front of his jacket and reaching into it with his right hand.

"Those who were in the staircase ran up the stairs and away from him. Callum chased after them and fired a gun on two occasions."

Robel was found on the third floor by the others and he had been hit by both bullets. One of them hit him in the leg but the other went into his back and through his liver, lungs and heart.

Firearms experts concluded the murder weapon was a blank firing Mac 10 style sub-machine gun which had been converted to fire live rounds.

After CCTV footage was studied both men were arrested on October 4.

Callum refused to say where he was on the night while Edwards eventually told police: "I deny murder. I feel upset for the man's family because my mum passed away when I was young."

When police took Callum's mobile phone they discovered his own number was stored against the nickname "Kill".

A number of draft text messages referred to guns and spoke of him being "ready to ride on a mission" and said he would not "stop till I mini-mac a nigger... you see he'll be dead by morning. Your boy's got whacked up," the court heard.

Mr Hilliard said: "These describe killing someone with a gun using a Mac machine gun with chrome nine bullets and riding on a mission."

Mobile phone records showed both defendants used their phones in the vicinity of the flats within 10 minutes of the murder but jurors were told how the prosecution had been unable to come up with a motive for the killing.

"Why did this shooting happen?" Mr Hilliard said to jurors. "We can't help you. The prosecution don't have to prove why a defendant committed a particular crime just that the defendant did in fact commit it. The evidence demonstrates that the men were in it together."

The trial continues.