The assault in Mpeketoni began on Sunday night as residents watched World Cup matches on television and lasted until early yesterday, with little resistance put up by Kenya's security forces.
Authorities blamed al-Shabab, Somalia's al-Qaeda-linked terror group, who have promised to carry out terror attacks to avenge the Kenyan military presence in Somali.
Like the gunmen who attacked Nairobi's Westgate Mall last year and killed 67 people, the Mpeketoni attackers gave life-or-death religious tests, killing those who were not Muslim.
Anne Gathigi said: "They came to our house and asked us in Swahili whether we were Muslims. My husband told them we were Christians and they shot him in the head and chest."
Another resident, John Waweru, said his two brothers were killed because the attackers did not like that they did not speak Somali.
At the Breeze View Hotel, the gunmen pulled the men aside and ordered the women to watch as they killed them, saying it was what Kenyan troops are doing to Somali men inside Somalia.
The US, UK, France, Australia, and Canada have all recently upgraded their terror threat warnings for Kenya.