The son of a Kenyan government official was one of the masked gunmen who killed nearly 150 at a university last week, the interior ministry said on Sunday, as Kenyan churches hired armed guards to protect their Easter congregations.
Pope Francis decried Thursday's attack in his Easter Sunday service, praying for those killed by Islamist gunmen who hunted down Christians while sparing Muslims.
At one church in the Indian Ocean port city of Mombasa, worshippers were evacuated and a bomb disposal unit deployed due to a suspicious vehicle parked outside the church.
Interior Ministry spokesman Mwenda Njoka said Abdirahim Abdullahi, son of a government official in the northern Mandera county bordering Somalia, was one of four gunmen who stormed the college campus in northeastern town of Garissa.
"The father had reported to security agents that his son had disappeared from home... and was helping the police try to trace his son by the time the Garissa terror attack happened," Njoka told Reuters in a text message.
President Uhuru Kenyatta on Saturday said the planners and financiers of Islamist attacks were "deeply embedded" within Kenyan communities and urged Muslims to do more to fight radicalization.
A Garissa-based official said the government was aware Abdullahi, a former University of Nairobi law student, had joined the militant group al Shabaab after graduating in 2013.
"He was a very brilliant student. But then he got these crazy ideas," said the official.
Al Shabaab group said the assault on Garissa, some 200km (120 miles) from the Somali border, was revenge for Kenya sending troops into Somalia to fight alongside African Union peacekeepers against the al Qaeda-aligned group.
The militants have threatened to turn Kenyan cities "red with blood" and police have stepped up security at shopping malls and public buildings in the capital Nairobi, and the eastern coastal region which has been prone to al Shabaab attacks.
The Garissa assault has further strained the historically cordial relations between Kenya's Christian and Muslim communities, which have deteriorated due to frequent Islamist attacks on Christian priests and churches.
Kenyan priests said they feared churches could be targeted on Easter Sunday, the main liturgical feast in the Christian calendar.
"We are very concerned about the security of our churches and worshippers, especially this Easter period, and also because it is clear that these attackers are targeting Christians," Willybard Lagho, a Mombasa-based Catholic priest and chairman of the Coast Interfaith Council of Clerics (CICC), told Reuters.
He said churches Mombasa were hiring armed police and private security guards for mass on Easter Sunday. Christians make up 83 percent of Kenya's 44 million population.
Guns in churches
In Nairobi's Holy Family Basilica cathedral, two uniformed police officers armed with AK-47 rifles manned the entrance gate. One officer said more plain clothes officers were inside.
Three private security guards frisked churchgoers with hand-held metal detectors, while a fourth guard used a mirror to check for explosives underneath cars.
"Everyone is anxious and you never know what will happen next, but we believe the biggest protector is God and we are praying," said Samuel Wanje, 27, a youth member at the church.
In Garissa, where masked gunmen in 2012 killed more than a dozen people in simultaneous gun and grenade raids on two churches, six soldiers guarded the town's main Christian church and about 100 worshippers ahead of Sunday mass.
Kenyatta is under pressure to halt Islamist attacks that have ravaged Kenya's tourist industry. A dusk-to-dawn curfew is in force along Kenya's 700km border with Somalia and helicopters monitor its palm-fringed coast, popular with Western tourists and the scene of Islamist attacks in the past.
Coastal Region police chief Robert Kitur told Reuters extra uniformed and plain-clothes police officers had been deployed.
Late on Saturday, 613 students and 50 staff from Garissa University College arrived in Nairobi to an emotional welcome by parents and relatives. Parents of missing students attempted to identify bodies at the city's mortuary.
Garissa was the most deadly attack on Kenyan soil since al Qaeda in 1998 bombed the U.S. embassy in Nairobi, killing more than 200 people and wounding thousands of others.