LONDON (Reuters) - British police said they had arrested a Libyan man on Thursday over his suspected role in the murder of unarmed policewoman Yvonne Fletcher, who was shot dead outside the Libyan embassy in London in 1984.

Police constable Yvonne Fletcher is seen in an undated file photo. British police said they had arrested a Libyan man on November 19, 2015 for the 1984 murder of Fletcher who was shot dead outside the Libyan embassy in London. REUTERS/Metropolitan Police/Handout via Reuters

Fletcher, who was 25 and had joined the police aged 19, was hit in the back by a shot fired from the embassy while she was policing a demonstration by Libyan dissidents against Muammar Gaddafi, who then ruled the North African country.

The shooting triggered an 11-day siege of the building by London’s Metropolitan Police, the deportation of 30 Libyans in the embassy and the severing of diplomatic ties between London and Tripoli.

The shot that killed Fletcher was one of several fired from the embassy and 10 Libyan anti-Gaddafi campaigners suffered gunshot wounds. Police believe two weapons, a pistol and an automatic weapon, were used in the incident.

“This is the first significant arrest in this investigation” Richard Walton, who heads London police’s counter-terrorism command, told reporters. “We do believe today’s arrests mark a significant turning point.”

Walton said a man in his 50s had been arrested in southeast England on conspiracy to murder and money laundering offences. A woman in her 40s and a man in his 30s, also Libyan, were also arrested for money laundering.

The suspects were in police custody, and searches were continuing at several addresses across Britain, police said.

Slideshow ( 2 images )

The arrest of the murder suspect comes as a result of new information obtained since the fall of Gaddafi in 2011, with London officers having made seven visits to Libya since then.

CONSPIRACY TO KILL POLICE

Police believe there was a deliberate conspiracy to murder officers and Gaddafi opponents, and that those involved in a rival, pro-Gaddafi, counter-demonstration were receiving instructions from within the building.

“We believe that the incident was part of the so-called ‘stray dogs campaign’ being orchestrated from Libya to attack overseas dissidents and their interests during that time,” police said in a statement.

They said they wanted to speak to those demonstrating on the day and those inside the embassy and have launched their biggest ever Facebook campaign as part of a global appeal for more information. Police are also offering a 50,000-pound ($76,000) reward for information leading to the capture and prosecution of those involved.

“Witnesses may now be living in other countries all these years later,” Walton said. “We are hoping that with the passage of time and with allegiances changing, that witnesses who have not spoken to us will examine their consciences and come forward.”

Detectives released 14 images of individuals they are keen to identify, as well as video footage of the demonstration and shooting.

“The day Yvonne was shot remains one of the saddest and darkest days in the history of British policing,” said Walton. “We have never lost our resolve to solve this case and to bring to justice those who conspired to commit this act of murder.”

Fletcher’s family issued a statement appealing for information.

“Recently we have had to come to terms with another loss through the death of Yvonne’s father, Tim,” the statement said. “His one regret in life was that no one had been arrested in connection with the murder of his daughter and never witnessed any justice.”