Last-known footage released of missing woman Lisa Dorrian

For the first time, police have released CCTV footage of the missing woman Lisa Dorrian which was filmed just days before she disappeared 20 years ago.

Ms Dorrian, who is believed to have been murdered, has not been seen since she went to a party in Ballyhalbert, County Down, at the end of February 2005.

Police said on Thursday that the CCTV recording is "the last known footage of Lisa".

Her family have joined police to reissue their appeal for information, saying: "Twenty years of secrecy could be ended with a single phone call."

Ahead of the anniversary of the Bangor woman's disappearance, a reward of £20,000 has been offered to anyone who has information leading to a conviction for her murder or to the recovery of her body.

Ms Dorrian, who was 25 and from Bangor, was last seen at 05:00 GMT on 28 February 2005, having attended a house party at a caravan park in Ballyhalbert.

Her handbag and belongings were discovered at the party.

No one has ever been convicted over her disappearance and, despite many land and sea searches, her body has never been found.

The Police Service of Northern Ireland (PSNI) began treating the case as a murder inquiry almost immediately after her disappearance.

Det Ch Insp Kerrie Foreman said she hoped releasing the CCTV footage would "jog memories and to encourage anyone with information to speak up".

"Twenty years have now passed. That's 20 long years of unimaginable torment for a loving family," she said.

"Yet, despite their pain, they've never given up their search for answers and, likewise, our determination has remained steadfast."

The officer said those responsible for her murder "have not yet been held to account" and she appealed to witnesses to "do the right thing".

The Dorrian family, including her younger sister Joanne, have led a high-profile campaign in a bid to find Lisa's body and bring her killers to justice.

At Thursday's press conference, Joanne Dorrian said: "Lisa lost her life at the hands of people she knew and trusted."

She said she would have "laughed and joked with these people" on the night she went missing and would "never have imagined" they would have caused her harm.

"Our family has never been the same since the day we got the news that Lisa went missing," Joanne added.

"Our mum went to her grave never knowing what happened to her beautiful first-born daughter."

She said her family's grief and pain has been "all consuming" and her "absence in all of our lives has grown over the years".

The Dorrians are now stepping up their appeal with a new digital billboard and bus shelter poster campaign.

Joanne Dorrian told reporters that her older sister had been "denied all of her hopes and dreams" but the family "hope to see Lisa's murderers in court one day soon".

In a direct appeal to those who know the killers, she said: "Twenty years of secrecy could end with a phone call, a letter, a message.

"Please tell us where Lisa is."

Det Ch Insp Foreman said people who know what happened, but who are reluctant or frightened to come forward, "must surely have a troubled conscience".

"Lisa wasn't just a name or an image on a photo or screen," she said.

"She was a real person – a young woman with a family that love and continue to miss her dearly.

"They deserve to know what happened to her and they deserve justice."

The officer added that witnesses can be "assured that information can be passed, with 100% anonymity, to the independent charity Crimestoppers".

"With Crimestoppers, calls are never recorded, there's no caller line display or 1471 facility, and computer IP addresses can never be traced," she explained.

"I am asking you to take this opportunity to do the right thing and speak up."