A 20-year-old driver accused of killing a mother during an "impromptu race" with another driver allegedly left the scene after the fatal crash to attend a birthday party.

Joseph Fettah was allegedly driving up to 70mph in an illegal road race against 24-year-old Jamie Oaten after the two pulled up to traffic lights together. Oaten, a bricklayer, then struck 30-year-old Jenna Miller with his Audi A5 as she pulled out of a petrol station in Barry, South Wales.

The mother-of-two was cut from her Mazda 6 car before being taken to hospital, where she died, Metro reported.

Fettah, a security worker, did not speak to police after the fatal crash on 27 September and instead had a friend pick him up and went to a party.

He told a jury at Cardiff Crown Court that he and Oaten were not friends and had never met each other, The Sun reported. Fettah denied he tried to race Oaten, adding: "I thought to myself that he was going a bit too fast."

Fettah said he was driving a VW Golf owned by his father's company and was on his way to have repair work done on both rear tyres.

Fettah told the jury why he left after the crash , saying: "I didn't want to get myself involved. I didn't know that anyone was seriously hurt at the time."

He said he went to the birthday party but did not drink and left early due to shock. "I was going off to a birthday party. I didn't know it had been a fatal road accident. I didn't drink and I left within two hours. I was quite shocked," he said.

"I was shocked by what I saw—the Audi was going to fast."

Matthew Cobbe, prosecuting, said a collision expert concluded that both men were accelerating at maximum speed before the crash.

"Jamie Oaten is not solely responsible for the collision. He was driving at excessive speed because he got himself involved in an impromptu race with Joseph Fettah," Cobbe said.

"That impromptu race led to the collision and the death of Mrs Miller."

Cardiff Crown Court heard that Oaten has pleaded guilty to causing death by dangerous driving, the Metro reported. Fettah, meanwhile, denied causing death by dangerous driving but was found guilty.

Both men are awaiting sentencing.