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Sayyid Azim, Associated Press
Kenyan Muslim women wearing the Hijab wait in a queue to be checked by security at Kenyatta International Conference Centre during the Islamic Conference in Nairobi, Kenya, Sunday, April 5, 2015. Tight security was in force for the three day Islamic Conference following the Thursday killings by Al-Shabab gunmen at a university in northeastern Kenya.

GARISSA, Kenya — The son of a Kenyan government official was one of the gunmen who attacked a Kenyan college where 148 people were killed, authorities said Sunday.

Abdirahim Mohammed Abdullahi, one of the Islamic extremists who attacked Garissa University College, was the son of a government chief in Mandera County, Interior Ministry spokesman Mwenda Njoka told The Associated Press.

The chief had reported his son missing last year and said he feared that he had gone to Somalia, said Njoka. All four attackers were killed by Kenyan security forces on Thursday, said police.

Abdullahi graduated from the University of Nairobi with a law degree in 2013 and was viewed as a "brilliant upcoming lawyer," according to Njoka. It is not clear where he worked before he disappeared last year, Njoka said.

To prevent an escalation of Islamic radicalization in Kenya, it is important for parents to inform authorities if their children go missing or show tendencies of following violent extremism, said Njoka.

The four gunmen entered the Garissa campus on Thursday and slaughtered students. The gunmen were all killed more than 12 hours after the start of the attack. Somalia's al-Shabab Islamic militants claimed responsibility for the attack saying it is retribution for Kenya deploying troops to Somalia to fight the extremist rebels.

The news that one of the attackers was Kenyan highlights the challenges faced by the government in preventing extremist attacks. The danger comes not only from neighboring Somalia from where the Islamic militants of al-Shabab launch attacks, but also from within Kenya.

Kenyans make up the largest number if foreign fighters in al-Shabab, according to experts. Hundreds of Kenyan youths have trained with al-Shabab and then have returned to Kenya, posing a major security threat, according to former police chief Mathew Iteere.

Kenya's government has said another source of instability is the refugee camps with more than 423,000 Somali refugees.

There are several questions about the security response to the Garissa attack. Army barracks are just 500 meters (540 yards) from the college but troops did not succeed in quelling the attack.

Police waited for seven hours before sending a special tactical unit into Garissa college to fight the extremist gunmen, Kenya's Daily Nation newspaper reported Sunday. When the specially-trained police unit finally went into the college campus it took them only 30 minutes to kill the four al-Shabab gunmen and stop the siege, said the paper.

The newspaper's front page article questioned why the Interior Minister and police chief were flown to Garissa from Nairobi before the tactical team.

Before the attack on Garissa college, northeastern Kenya has had other attacks by al-Shabab in which Christians were separated from Muslims and then killed. Some Christians are questioning whether they should stay in northeastern Kenya near the border with Somalia.

In the wake of the attack, grieving Christians prayed, sang and clapped at an Easter Sunday service at a Catholic church in Garissa.

Security forces patrolled the perimeter of Our Lady of Consolation Church, which was attacked by militants almost three years ago. Grenades lobbed at the building sprayed shrapnel into the interior, injuring some worshippers. Another Garissa church was also attacked that day and 17 people were killed.

Sunday's ceremony was laden with emotion for the several hundred members of Garissa's Christian minority, which is fearful following the attack by al-Shabab, a Somalia-based Islamic extremist group. The gunmen who attacked Garissa University College on Thursday singled out Christians for killing, though al-Shabab has a long record of killing Muslims.

"We just keep on praying that God can help us, to comfort us in this difficult time," said Dominick Odhiambo, a worshipper who said he planned to abandon his job as a plumber in Garissa and leave for his hometown because he was afraid.

"Thank you for coming, so many of you," Bishop Joseph Alessandro said to the congregation. He said some of those who died in Thursday's attack would have been at the service, and he read condolence messages from around the world.

Alessandro saw a parallel between the ordeal of Jesus Christ, which Easter commemorates, and that of Garissa.

"We join the sufferings of the relatives and the victims with the sufferings of Jesus," he said. "The victims will rise again with Christ."

Alessandro said there has been an increase in insecurity because of al-Shabab.

"You don't know who they are. They could be your neighbors," he said. A heavy security presence only helps up to a point and more intelligence on the militants is needed, he said.

Al-Shabab warned Saturday that Kenyans will face more violent attacks.

"No amount of precaution or safety measures will be able to guarantee your safety, thwart another attack or prevent another bloodbath," said al-Shabab.

Following the extremists' threats, Kenyan President Uhuru Kenyatta vowed to take harsh measures against the Islamic militants.

In a nationally televised address, Kenyatta said his administration "shall respond in the severest ways possible" to the Garissa attack.

"We will fight terrorism to the end," said Kenyatta, who declared three days of national mourning.

Five people have been arrested on suspicion of involvement in the Garissa attack, a Kenyan official said.

AP writer Tom Odula contributed to this report from Nairobi, Kenya.