Pumwani, Kenya (CNN) -- Asha Mohamed sits in her cramped room in Pumwani slum clutching a tiny photo of her son, Harun. He's dressed in a blue-striped tie framed by a crisp white T-shirt -- a typical 15-year-old Kenyan high school student. 

But in September he vanished. "Harun woke up very early and asked his sister "what time is it?" says Asha. He kept on asking her again and again. Then, at four in the morning, he left the house." 

In her heart, Asha knew where he had gone, but the text messages later confirmed it. Harun left his school and home in Kenya to fight for al Qaeda-linked Al Shabaab. 

"It started when he was 14. He came to me many times and said "mom, I am going to Somalia to fight Jihad." I thought he was just playing." 

For years, Al Shabaab has targeted Somalis abroad to fight in their campaign to overthrown the weak transitional government. Now Kenyans, with no ethnic link to Somalia, are joining the Jihad. 

According to a recent U.N. report, there are "extensive Kenyan networks linked to Al-Shabaab, which not only recruit and raise funds for the organization, but also conduct orientation and training events." 

Many of those events centered on Pumwani, a largely Muslim slum in Nairobi. Here, residents and religious leaders speak of a charismatic young Kenyan Sheikh that arrived from Mombasa. 

They say he bravely stood up to corruption, promoted the Quran, and generously handed out scholarships to young men. And he stoked their passion for Al Shabaab. 
What kind of support do the Kenyan networks provide the terrorist group?
 which not only recruit and raise funds for the organization, but also conduct orientation and training events