Bardo attackers Isis Tunisia
In this still from CCTV footage of the Bardo museum attack, two gunmen appear to encounter another mystery figure who they allow to walk awayYouTube/Brunette Tn

A third gunman was involved in the attack by Islamic State (Isis) terrorists at Tunisia's Bardo museum in which 25 people died, says Tunisian President Beji Caid Essebsi.

The president made the announcement following the release of CCTV footage of two attackers prowling around the museum in search of victims. At one point they bump into a mystery figure wearing a backpack descending a flight of stairs. The three appear to acknowledge one another before the third man walks away in the opposite direction.

"There were certainly three attackers… there is one who is on the run, he won't get far," said President Essebsi in an interview with France's iTele network from inside the museum. The network also

The network also broadcast dramatic footage of the response of Groupe des Forces Spéciales – the Tunisian army's special forces unit – to the massacre.

Twenty-three people, including British solicitor Sally Jane Adey, 57, were killed when terrorists armed with machine guns attacked the Bardo Museum on Wednesday (18 March).

Sally Jane Adey Tunis victim
Sally Jane Adey from Shropshire was among those murdered in the Bardo museum attack by IsisFacebook

Adey was visiting the museum with her husband, who witnessed her death.

Josep Lluis Cusido, who is the mayor of Vallmoll, hid behind a pillar as two men went on their killing spree.

"They looked to see how they could inflict the most damage possible. I saw one group who was in the museum who took refuge in a room… They went in there and machine-gunned them all," Cusido told AP. He went on to describe the horrific scene that followed when he tried to help a woman victim.

"She'd been hit by bullets and I tried to help her but couldn't and then ran to hide. There are scenes that I fear will remain in my head for a long time."

Amid the scenes of carnage, Casido noticed that both attackers seemed young.

"From what little I saw – because I obviously wasn't going to stop to take a selfie with them coming – the terrorists were young."

Two attackers – Hatem Khachnaoui, 26, and 20-year-old Yassine Laabidi – died in a shoot-out with the special forces operatives.

Islamic State (Isis) says has claimed responsibilty for the attack. The authorities in Tunisia have announced an investigation into possible security lapses that allowed the men to enter the museum through a lightly monitored access point.

The authorities in Tunisia have announced an investigation into possible security lapses that allowed the men to enter the museum through a lightly monitored access point.