It happened around 11:30 Saturday night on the 100 block of West 9th Street.
A routine patrol officer reported seeing a suspect inside a vacant store.
The officer confronted the man who refused to listen and fled further into the store.
The incident continued into the basement of the building, where police say the suspect physically assaulted the officer.
After being unable to subdue the man, the officer was forced to fire his weapon.
The suspect - a man in his 20s - was pronounced dead at the scene.
The shooting is being investigated by Wilmington Police and the Attorney General's Office.
The officer was placed on Administrative Leave pending the investigations as per standard Departmental Policy.
No word yet on the slain suspect's identity.
