SHOOTER AND VICTIM WERE NEIGHBORS

The Maryland shooting happened around 11:15 am EST (1615 GMT) on the mall's upper level just above the food court. The mall, which has more than 200 stores, was crowded with weekend shoppers; many took shelter after hearing the shots or seeing people fleeing.

Police, who were in the area on another case, responded to the emergency calls within two minutes and found all three bodies either in the store or just outside it.

Aguilar had a backpack filled with crude explosives, and authorities were initially concerned he had booby-trapped himself, McMahon said.

"These were homemade devices consisting of flash powder and household items, so they're not very sophisticated," McMahon said. Police believe Aguilar legally bought the shotgun himself last month in nearby Montgomery County.

Overnight, police searched Aguilar's home where they found more ammunition, and seized computers, including a journal.

"He does express some general unhappiness with his life," McMahon said of the journal.

McMahon said he could not yet give further information about Aguilar, including whether he worked or was a student.

Aguilar lived less than a mile (1.6 km) away from Benlolo, the female victim, in a quiet middle-class neighborhood with tree-lined streets in College Park, which is home to the University of Maryland's flagship campus.

There was no answer at Aguilar's address. Neighbors said he lived there with his mother and possibly a sister, and that the family, who had only moved in within the last couple of years, kept to themselves.

Neighbor Megan O'Reilly said she interacted with them only a couple of times. "The house, when I visited, looked immaculately kept on the inside," she said. "They were not very engaging as neighbors."