Forgetting his wallet cost him his life.

An immigrant NYU lab technician, who is also a medical student and father of six, was beaten to death Thursday night by a manic neighbor who was seen earlier shadow-boxing in the hallway of their 11-story Bronx apartment building.

Bakary Darboe, 46, was just about to walk out of the East 156th Street building in Melrose on his way to class at Mercy College when he realized he had forgotten his wallet and took the elevator back up to his 9th floor apartment.

Darboe was riding the elevator back to the ground-level when the doors opened at the 7th floor at around 5 p.m. and he was suddenly ripped out into the hallway by career criminal Junal Jordan, 40, police sources said.

The brute, who has 20 prior arrests, allegedly pummeled Darboe with his fists, beating him senseless, and may have used an unknown object on the victim as the he begged him to “Get off me!” according to police.

Jordan, who lives on the 7th floor, was shadowboxing in the hallway just before the horrifying incident, cops said.

A neighbor witnessed the beginning of the assault and quickly shut the door.

After killing Darboe, a native of Gambia, the suspect fled the Melrose building but was nabbed a few blocks away by police who found him in blood-soaked clothes, cops said.

When police questioned Jordan – who has a lengthy rap sheet dating back to the 1990s on charges including drug possession, robbery and reckless endangerment – he acknowledged that he got in a fight in the building, sources said.

The suspect quickly lawyered up and is currently being questioned by investigators at the 40th Precinct station house. Charges were pending.

Police believed that the victim and his attacker did not know each other.

Meanwhile, more than a dozen of Darboe’s grieving family members gathered inside his apartment Friday wearing traditional Gambian garb.

“He’s a very kind man, humble. He’s religious. He loved his family, really. He’s a great man. We cannot forget about him,” said the victim’s oldest brother, Mbemba, 61.

Darboe, a devout Muslim who belonged to the local Gambia Islamic Society and has been working as a lab technician at NYU for five years, immigrated to the US about a decade ago, the older brother said.

The slain man’s 6-year-old daughter Jakong said, “He always helped me with my homework.”

Commenting on the attack, Mbemba said, “We can forgive, but we cannot forget as Muslims.”

Our editors found this article on this site using Google and regenerated it for our readers.