Mohamed Al Lal, who was arrested on Saturday, is suspected, along with his brother Farid and another pair of brothers, Anuar and Radouan Alli Amzar, to have been part of a terrorist cell, which was planning attacks in Spain.
Mohamed Al Lal had worked as a waiter at the ice-cream parlour, named Firenze, for seven years and had never raised suspicions among his co-workers.
"We can’t believe it, to be honest, we feel very bitter about it," Nicola Cecchi, owner of Firenze ice-cream parlour, told Spanish daily, El Mundo.
A photo has been released in El Mundo of Mohamed Al Lal, smiling with his colleagues and posing with a Roscón de Reyes, a traditional ring cake eaten in Spain on the Epiphany.
Only three weeks later he was being arrested as armed police stormed his house in the El Príncipe area of Ceuta, said by Spanish daily El País, to be 'one of the most dangerous areas in Spain'.
"He was never off sick, never late", Cecchi told Spanish press, “but of course, I have no idea what my staff are getting up to outside of work hours."
The Spanish interior ministry said the four men had "a very similar profile" to the killers in the recent Islamist attacks in Paris, but made no material link between the two cases.
The four were inspired by online messages from the armed group calling itself Islamic State (IS), which controls parts of Iraq and Syria.
"They formed part of a jihadist cell fully prepared and willing to launch an attack in Spain," an interior ministry statement said.
Police seized a nine-millimetre automatic pistol and machetes among other items during dawn raids on two properties.
They were the latest in a string of arrests in Ceuta and Spain's other north African territory, Melilla, where authorities have been monitoring suspected extremist cells.
Separately, Spanish authorities are investigating suspects linked to the attacks in Paris and other foiled plots in Belgium, who are said to have travelled to Spain.
Spanish police have arrested about 50 suspected jihadists over the past year, the ministry said this month. Many of them are suspected of planning to join IS.
Fearing a rise of "homegrown" and "lone wolf" extremists in Spain, the government has been cracking down on their recruitment online.
On March 11th, 2004, Al-Qaeda-inspired bombings killed 191 people in an attack on Madrid commuter trains.