The family of murdered policewoman Yvonne Fletcher said it is "time this case was closed" - but 30 years later they added it seems they are "no closer to achieving justice".
The family statement comes after a memorial service in St James's Square, central London, marking the 30-year anniversary of WPc Fletcher's death.
Members of her family joined her friends and colleagues in remembering the officer, who was shot dead outside Libya's London embassy on April 17 1984.
No one has ever been brought to justice for the killing but Scotland Yard detectives have never given up hope of identifying the culprit - and Metropolitan Police commissioner Sir Bernard Hogan-Howe reiterated their determination today.
"At the end of the day, Yvonne Fletcher's parents lost their daughter.
"Her sister lost a sister. We lost a colleague, and we're determined to make sure we catch the person responsible," he said.
In a statement, the family said: "Thirty years ago today, Yvonne was shot and killed outside the Libyan People's Bureau in St James's Square. To many it may seem like a fading memory but to the family it is as clear as yesterday.
"We have had to move on with our lives but it is difficult to move forward when the past remains unresolved. Closure is important to the family so that we can remember Yvonne as the happy caring person she was.
"We can look back and wish things had been handled differently but here we are 30 years later, having dealt with numerous governments and a dozen or more foreign secretaries and it seems no closer to achieving justice for Yvonne.
"Our desire for justice is as strong as ever and we continue to support the Metropolitan Police in their ongoing investigation. The truth about what happened 30 years ago is just as important to us today as it was then and we call upon the current Libyan government to enable the police to complete its investigation.
"It is time this case was closed, 30 years of being in the news and dealing with the pressure of media attention takes its toll on all the family, more than you will ever know."
Following a two-minute silence, the family laid floral tributes to the 25-year-old at the spot where she was gunned down.
Ms Fletcher was one of 50 officers policing a protest against Colonel Gaddafi's regime outside the embassy when she was hit by a burst of gunfire from a first-floor window.
Investigators believe the bullets, which killed her and injured 10 protesters, were fired by a sniper who intended to hit protesting Libyan dissidents.
Her death led to an 11-day siege of the building and the severing of diplomatic links between the UK and Libya.
Sir Bernard said the investigation has "never stopped", adding: "We're determined to make progress, and I'm confident we're making good progress."
In 2012 Scotland Yard sent a team of officers to Libya to continue their investigations into the murder.
More than 50 people paid their respects at the memorial, and among them was Ms Fletcher's friend and colleague John Murray who has spent the last 30 years campaigning for justice.
"Today is a day of remembrance, but then of course it's a day of celebration as well.
"We're here today with all Yvonne's former colleagues, her friends, her family. We're here to pay our respects, and really to achieve some sort of justice for her at the end of the day.
"Justice which, certainly I think over the last 30 years, has been severely lacking," he said.
Mr Murray, from Aberdeen, said he is still as passionate today about getting justice as he was three decades ago.
"I will get justice for Yvonne Fletcher. There's no doubt about that at all," he said.
Mr Murray recalled being in the ambulance with Ms Fletcher and telling her he would find out what happened.
"Bearing in mind that those were the last words she heard before she died, that's a promise I made to her and a promise I'll keep," he said.
Mr Murray said he believed the Metropolitan Police and the UK Government have "lacked the commitment" in solving the murder.
"That may be for a variety of reasons. I believe it's because of various secret deals, various oil deals, and various trade deals with Libya," he said.
Mr Murray described Ms Fletcher as "bright, cheerful, friendly", adding: "Couldn't do enough for people."
He said as a policewoman she was "very fair" and "very polite".
"People would come into the police station and ask for her," he said.
Mr Murray added that she was held in high esteem by everybody.
When asked about Mr Murray's beliefs, Sir Bernard said: "John is very passionate about this case, but he's no more passionate than I am."
Ms Fletcher's sister Heather Allbrook read a poem at the short service and the sun shone for the duration.
Late film director Michael Winner founded the Police Memorial Trust as a result of Ms Fletcher's murder.
He was represented today by his widow Geraldine Winner, who addressed the crowd.
"Michael would be so proud to know that 30 years after Yvonne's passing the Trust lives on and we gather to remember her again," she said.
Also present at the memorial were men who were at the protest on the day Ms Fletcher was killed and who were also struck with bullets.
Abduhakim Naas said that while they survived, and have gone on to live their lives, Ms Fletcher "has been denied all of this", adding: "It makes us feel guilt in a way. It should have been one of us."
Salah Gaddafi said: "We took a risk but she wasn't taking any risk. She was just doing her job."
The men laid flowers at the memorial, with a note that said: "As two of the Libyan protestors who were injured that 17th April 1984, we shall never forget or cease to regret WPc Yvonne Fletcher's sacrific (sic). We offer this wreath in honourable memory of one who fell on home soil but in a foreign war."
The memorial to Ms Fletcher in St James's Square was unveiled by then-prime minister Margaret Thatcher in 1985.
Libyan prime minister Abdurrahim El-Keib made a historic visit to the spot in May 2012.
Mr El-Keib visited the scene after it was announced a team of detectives from the Metropolitan Police would fly to Libya to continue their investigations into the unsolved murder.
The Libyan premier paused and bowed in front of the memorial to Ms Fletcher and laid a wreath of white roses and carnations at the spot.
Sir Bernard added: "The anniversary of Yvonne's murder will always remain a very sad day for the Metropolitan Police and a tragic event in policing history.
"Today serves as a reminder of the very real risks police officers face on a daily basis protecting London and the MPS remains committed to identifying and bringing to justice those people responsible for killing Pc Fletcher."
Following the restoration of diplomatic relations between the UK and Libya a joint investigation by the MPS and the Libyan authorities was started and this continues.
Detectives from the MPS inquiry team have visited Libya several times and met officials from the Libyan investigation team.
They last visited Libya in January 2014 and a number of times before that.
MPS detectives continue to seek the assistance of the Libyan judiciary to further their investigation through international letters of cooperation and visits, the Met said.