MARRAKECH, Morocco - A messy heap of Moroccan pastries sit in a shattered glass display case. Twisted nails, strips of clothing and mobile phone parts have been collected and placed in rows of jars. Tourist maps and a charred Douglas Adams' novel lie in clear plastic evidence bags, while the walls and floors bear the blood stains and nail-sized scars of a bomb blast that took the lives of 16 people days earlier.

Investigators hosted journalists Saturday at the devastated remains of the Marrakech cafe where a terrorist detonated a bomb on Thursday, killing mostly Western tourists and injuring more than two dozen more. Seven French, two Canadians, two Moroccans, a Dutch and a Briton have so far been identified as being among the dead.

The attack has shaken the relatively peaceful North African country, that drew nearly 10 million tourists last year to its sandy beaches, desert and mountain landscapes, and historic sites.

A visibly shaken King Mohammed VI earlier emerged from a long convoy of black Mercedes sedans to pay a sombre visit to the scene, underscoring the importance of tourism to Morocco's economy. It came just weeks after he promised constitutional reforms to shepherd in more democracy amid a push across the Arab world.

As thousands of people cheered and waved his portrait, or the Moroccan flags distributed before his arrival, he denounced Thursday's attack as "cowardly" and "criminal," saying it would "only strengthen the Moroccan people's will to stand up to whoever might attempt to derail the model that has been chosen for democratic (reforms) and development."

He also visited Ibn Tofail hospital, where two Moroccans and five French are receiving treatment, state news agency MAP reported. Five others -- two French, two Dutch and a Moroccan -- are being cared for at a Marrakech military hospital.

The Swiss foreign ministry said Saturday that two Swiss residents who were in the cafe at the time of the blast -- one of them a Swiss citizen, the other Portuguese -- are also missing. The two men were travelling with two female Swiss tourists it had said were seriously injured in the explosion.

Officials say no one has claimed responsibility for the blast, which burrowed a crater nearly 1-meter (3 foot) wide and nearly as deep in the second floor terrace of the Argana cafe that overlooks Djemaa el-Fna, the city's historic square. The cafe was renowned as a place for tourists to hang out -- to relax while gazing down on the square's snake charmers, fruit vendors and mystics.

Investigators said Saturday that the bombing looked like the work of professionals, and it was unlikely the perpetrator acted alone. Interior Minister Taieb Cherqaoui had said Friday that the attack bore the hallmarks of al-Qaida, though the terror group's eventual role has not been confirmed.

He said that the explosives used included the fertilizer ammonium nitrate and the chemical triacetone triperoxide, TATP -- used as a detonator in the 2005 London bombings that killed 52 people.

Investigators said early estimates suggested that the charge involved about 4 kilograms (9 pounds) of explosives, and it showered debris, body parts and shrapnel for dozens of yards out onto the square below. They have ruled out a suicide bombing -- saying the bomber had fled the scene by the time of the blast.

"From a distance, there are several possibilities (to set off a bomb)," Taoufiq Sayerh, head of the national scientific police squad, said. "Time-delay, infrared signal, even remote control... the investigations are continuing."

Morocco has been struggling to piece together who was behind the explosion. Sayerh said that the cafe did not appear to have security cameras on the terrace, and despite a police dragnet -- including checkpoints along the roads out of Marrakech -- the attacker or attackers have so far eluded authorities.

"This wasn't just anybody, doing any old thing," said one police investigator, speaking on condition of anonymity.

The bombing is the deadliest in Morocco since five near-simultaneous bombings by an Islamic extremist group left 45 people dead -- including a dozen attackers -- in Casablanca in 2003. Since then, Moroccan authorities have rounded up and jailed thousands of Islamists.

The North African affiliate of Osama bin Laden's network, Al-Qaida in the Islamic Maghreb, has its roots in neighbouring Algeria and has carried out bombings there and kidnappings in the Saharan regions to the south.

Morocco has had tense relations with Algeria over the years -- and a major thorn has been Moroccan-controlled Western Sahara. Its leading pro-independence group, Polisario Front, has refugee camps in Algeria.