Sky News published pictures of the killer, identified on Saturday as 23-year-old Abu Yahya al-Qayrawani, strolling along the shoreline Kalashnikov in hand, with sun loungers and inflatables behind him.
Dressed in black shorts and T-shirt, he is seen walking by dozens of unsuspecting tourists.
Witnesses recount that the gunman was “very very calm” as he began shooting at holidaymakers, having hidden his weapon inside a parasol.
The pictures were released as it was confirmed there are at least 15 British victims of the atrocity.
Foreign Minister Tobias Ellwood warned that figure “may well rise” further, adding that it was “the most significant terrorist attack on the British people” since July 7, 2005, when 52 people were killed.
Mr Ellwood said this act of “evil and brutality” demonstrates why this kind of extremism has to be confronted “wherever this happens” at home or abroad.
Asked if he feared further attacks on Britons abroad, he said: “We always have to be vigilant wherever we are in the world and we are doing our utmost to work with the international community to make all our places of interest safer.”
British police have flown to the resort to help identify victims, consular teams are in hospitals and hotels looking after those affected, and he said had spent much of today on the phone with victims and families caught up in the “appalling attack”.
Meanwhile, Tunisia’s Prime Minister, Habib Essid, has announced a clampdown on security.
He said army reservists would be deployed to archaeological sites and resorts.
About 80 mosques accused of “spreading venom” will close within a week, he said.