The man has been identified in Kenya as Hassan Abdi Dhuhulow, a 23-year-old Somalia native whose family moved to Norway in 1999. Norwegian authorities have still not named him, and had previously not said whether they knew of him before the four-day siege of the Westgate mall that killed nearly 70 people in the Kenyan capital.
But Marie Benedicte Bjoernland, the head of Norwegian security service PST, told The Associated Press that the Norwegian suspect was well known to her agency and that it even tried to dissuade him from becoming a jihadist.
"We had several talks with him ... before he left Norway more than three years ago," Bjoernland said at PST's headquarters in Oslo. "Obviously we didn't succeed, but there was quite an effort put into the preventive side of this."
Bjoernland declined to give details of the conversations, and said the Norwegian "most likely" died in the attack, though PST investigators haven't confirmed that. The Kenyan government said Sunday it believes it has recovered the remains of the four gunmen seen in CCTV footage carrying out the attack.
Security camera images showed what appeared to be Dhuhulow and three other gunmen firing coldly on shoppers as they made their way along store aisles after storming the upscale mall.
The Somali Islamic extremist group al-Shabab claimed responsibility, saying the September attack was retribution for Kenya's military involvement in Somalia.
Dhuhulow's sister told AP last week that her brother went to the Somali capital of Mogadishu for a three-month visit in 2009, then moved to Somalia for good in March of the following year. She said she didn't believe he was among the gunmen seen in the footage.
Just days after Dhuhulow's identity became known, Norwegian police issued international alerts for two Norwegian-Somali sisters, ages 16 and 19, who told their family they were traveling to Syria to join the civil war. They were last spotted on the Turkish-Syrian border.
"We see a growing problem when it comes to people traveling to war zones, and specifically the last year we've seen a growing number of persons traveling to Syria," Bjoernland said.
She said between 30-40 people have left Norway to take part in the Syrian civil war, but added that the number is uncertain and may be bigger.
That conflict has attracted hundreds of foreign fighters from European countries, many of whom have joined Islamic militant groups. Western security services are concerned that they could pose terror threats when they return home with combat experience and terrorist training—and possibly traumatized.
"When they are radicalized and when they are determined to go, for instance to Syria or other conflict areas, we don't have many legal measures to stop them," Bjoernland said.
Norway just recently made it illegal to receive training from terror groups. But even with that law it is difficult for authorities to prove that a suspected want-to-be militant is traveling abroad to train with or join jihadist groups.
"We do preventive work. We talk to them. We try to persuade them not to go, because it's a dangerous journey," Bjoernland said. "I wish we were more successful. We have succeeded in turning some around from traveling. But quite a few have actually left."
She called on other parts of society, including parents, child protective services, police and Muslim leaders to intervene when young Muslims are at risk of becoming radicalized.