Police officers said they found a blackboard placed in a road near the killings that said “Raila Tosha,” which means “Raila’s enough,” and “Kick Christians out of coast,” suggesting a domestic source for the violence rather than a foreign one. Those implications, whether true or not, are bound to push the political temperature even higher.

Many Kenyans and security experts alike are confused about who is behind the attacks, which began last month with a full-fledged raid on what had been a sleepy coastal town.

At first, many believed the culprits were Shabab militants from Somalia, who have taken responsibility for the killings, including the attacks on Saturday night. In a radio address, the Shabab boasted that the same group of militants had attacked both villages and “disabled the enemy of God.” The Shabab promise to keep wreaking havoc in Kenya as long as the country has troops in Somalia. (Kenya sent troops into Somalia in 2011 in an effort to stabilize the country.)

But now it is not so clear who the killers are. The coastal areas hit recently are a hive of local grievances over land, ethnicity and economic opportunity. The Kenyan government is in the midst of building a huge, multibillion-dollar port in the same area, and many business interests are now jostling for a piece of the pie.

Last month, President Kenyatta attributed the attacks to “local political networks,” and the governor of the surrounding county was promptly arrested on suspicion of murder. Many people who know the governor insist that he is innocent. Some analysts, though, have speculated about whether local groups disgruntled with Mr. Kenyatta’s government might be cooperating with the Shabab to mount attacks against Kikuyus.

The most obvious victim is Kenya’s tourism industry, a pillar of the economy. Western governments, including the United States and Britain, have issued travel advisories, scaring away tourists. The Kenyan coast is usually packed in the summer with kite surfers, fishermen and sunburned European children digging holes in the sand. But now countless hotels have closed or nearly shut down, laying off legions of cooks, maids, waiters, drivers and many others who support their families with tourism jobs.