Investigators suspect he carried a laptop computer with a bomb concealed onto the plane, according to a source familiar with the investigation.
The source said Borleh apparently knew precisely where to sit and how to place the device to maximize damage. The source said, given the placement, the blast likely would have set off a catastrophic secondary explosion in the fuel tank had the aircraft reached cruising altitude.
The source added that investigators believe the attack was orchestrated by the al Qaeda affiliate Al Shabaab, although they are not certain that Borleh was a direct member of the group. No group immediately took responsibility for the act.
The bomb contained a military grade of the explosive TNT, according to the source, citing an initial analysis of residue recovered from the aircraft.
The blast happened Tuesday on Daallo Airlines Flight 3159 after it set off above East Africa.
Two people were injured before the pilot landed the Airbus A321-111 safely, a passenger said. Somali authorities later discovered a body near Mogadishu they believe fell from plane.
Pictures from the ground showed a hole in one side of the airliner, just above its wing and slightly smaller than one of its doors.
An airport official estimated the Daallo plane was between 12,000 and 14,000 feet high when the blast occurred not long after it took off from Mogadishu International Airport.
The pilot then flew the plane, which had originated in Jeddah on Saudi Arabia's Red Sea coast, back to the Somali capital.
Al-Shabaab has been behind some of the worst violence in recent years in and around Somalia
Some of it targeted tourists, such as last month's deadly attack on a beachside restaurant-hotel complex in Mogadishu. Young people also have been targets, as shown in the massacre at Kenya's Garissa University College. The general public also hasn't escaped the group's violence, as evidenced in a 2013 assault on an upscale mall in Nairobi.