The family of one of the two gunmen responsible for the massacre Thursday at Tunisia's Bardo National Museum says they had no reason to suspect anything was amiss on the day of the attack.

"If I knew, I would have stopped him," Mohamed Laabidi, the father of Yassine Laabidi, told VICE News outside the family's home in Tunis. "We are his family, the closest people to him, and yet we didn't suspect anything."

On the day of the attack, the 27-year-old Laabidi woke up, took coffee with his family, and then headed into the office where he worked as a deliveryman. He stayed only an hour before he disappeared at around 10am. When his managers tried to contact him later, they found he had switched off his phone.

When the family saw the hostage saga unfolding on the news at around 1pm Tunisian time, the Laabidi family had no idea their son was involved until the police showed up that evening.

Armed with Kalashnikovs, Laabidi and another young man, 19-year-old Saber Khachnaoui, killed at least 20 foreigners and three Tunisians. More than 40 others were injured in the attack. Some tourists at the museum saved their lives only by smearing blood on themselves and playing dead.

In the ensuing nationwide security crackdown, Tunisian authorities arrested more than 20 suspected militants, including 10 who were allegedly directly involved in orchestrating the Bardo attack.

Several people in Laabidi's neighborhood told VICE News he was a practicing Muslim, but did not show any obvious signs of extremism. They said he used to drink occasionally, though he gave it up in recent years. Young men in the Tunis neighborhood of El Omrane said Laabidi used to joke with his friends about girls. Most agree he must have been radicalized online. Many other details, however, remain elusive.

Laabidi's father was only able to answer a few questions before individuals that appeared to be plainclothes security officials told him not to say anymore and quickly ushered him away. He said the family was taken in for 24 hours of questioning on the night of the attack, and again for seven hours on Friday. He said they have barely slept and are in a state of shock.

Yassine's uncle, Abdel Malik Laabidi, offered more details.

A man and woman outside the Tunis' Bardo Museum, on Thursday 19 March, at a demonstration near the site of the terrorist attack.

Around December or Janaury, Yassine told his family he was going to Sfax, Tunisia's commercial hub, to look for work. In reality, the authorities say, he went to a training camp in Libya. His family confirms that they were suspicious of his story. Didn't he call them while he was out of town?

"Sure, there were telephone calls," his uncle told VICE News. "But we suspected he might be in Libya because the calls were made over the internet and weren't coming from Tunisian numbers."

The Islamic State has claimed responsibility for the attack in an audio recording posted online, but a rival group linked to al Qaeda has also staked a claim.

The attack has raised question about the extent to which international recruitment networks for many armed militant groups have managed to spread their tentacles in Tunisian society, recruiting young men (and, sometimes, women) to fight in Libya, Syria, and Iraq.

The al Qaeda-linked group Ansar al-Sharia, for instance, established itself in Libya and in Tunisia in 2012 in the aftermath of the 2010 Tunisian Revolution. Many Tunisians were angered that their leaders were apparently turning a blind eye to the rise of the militant group.

Members of Ansar al-Sharia would later be linked to both the attack on the US consulate in Benghazi in late 2012, and to two political assassinations in 2013 that caused major political upheaval in Tunisia. Some of the same people were linked to both the Tunisian and Libyan attacks.

Ali Harzi, a Tunisian who was arrested in Istanbul and deported to Tunisia, was released by Tunisian authorities in January 2013 and went on to be a key player in both political assassinations. Under growing public pressure, Ansar al-Sharia was finally outlawed by Tunisian authorities in mid-2013.

Some Tunisians are now asking whether the museum attack might have been avoided if the country's police and judicial system had handled previous investigations more thoroughly. There are also questions over why security at the museum, which is next door to the heavily secured parliament, was so lax.

While admitting that his nephew participated in the attack, Yassine's uncle also noted that the young man was one of many people who played a role in Tunisia's deadliest terror attack involving foreigners since a 2002 suicide bombing in the city of Djerba.

"It's true, Yassine carried out this attack, but Yassine was himself a victim," Abdel Malik told VICE News. "What about those who give them the money, who gave them the weapons and passports, who took care of the logistics?"