Armel Gnango claimed he had never fired a gun before
A man has been jailed for at least 20 years for the murder of a woman caught in a "Wild West" style shoot-out.
Magda Pniewska, 26, was shot in the head in New Cross, south London, in October last year.
The care assistant was talking on her mobile when she was shot. Her sister in Poland told the Old Bailey she heard Ms Pniewska's last breath down the phone.
Armel Gnango, 18, was jailed for life for murder when he was sentenced at St Albans Crown Court.
For the protection of the public, the judge also gave Gnango a minimum 12-year sentence for attempted murder and a five-year sentence for possession of a firearm. Both sentences are to run concurrently.
Mr Justice Cook told him: "The fact of the matter is that you went armed to find your man who then shot at you and a gun fight ensued.
"Either of you might have been killed.
"You plainly intended to kill the other and instead of either of you dying an innocent nursing assistant was killed instead."
The Old Bailey jury during the trial in May was told it was not Gnango's weapon which fired the fatal bullet but he was still responsible for the killing because he was involved in the gunfight.
The second teenager was also arrested but not charged, the court heard.
Prosecutor Brian Altman QC said: "In scenes reminiscent of the Wild West, Magda was to become the innocent victim of a gunfight by two total strangers.
"She was caught in the crossfire between two youths armed with handguns. Each had a score to settle.
Magda Pniewska was on the phone to her sister when she was shot
"The gunfight tragically ended the life of a young woman who had fearlessly given her life to caring for others."
Giving evidence, Ms Pniewska's sister Elzbieta Luby said she heard three or four shots before hearing her sister die.
"There was a short break between the third and fourth shot, like a moment's hesitation," she told the court.
"I asked Magda: 'What's happening, what is going on, who's shooting?' She said: 'Wait a minute, Ella.' The fourth shot came.
"I heard the last breath of Magda."
The conviction for murder of someone who was known not to have fired the fatal shot was described by the Crown Prosecution Service (CPS) as "unprecedented".
CPS lawyer Jane Scholefield said: "Even though the defendant did not fire the fatal round, and even though Magda Pniewska was not the intended target of either gunman, the defendant bears a joint criminal liability for her death.
"Each fired their guns with intent to kill at a time when there were bystanders present between them."