The neighbor says "they." Was there an accomplice? Or is she just confused? The story certainly seems to indicate that the perp was acting alone.
But if she was confused, you'd think the reporter would do something to correct her, or ask her what she meant.
There is a a natural tendency for acts of horrific evil or great import to be attributed to some nebulous "they". Many have speculated that many of the JFK conspiracy theories have arisen because nobody wants to believe that a loser like Oswald, by himself, could be responsible for the death of a President.
Perhaps the neighbor simply doesn't want to believe that such mayhem could have been caused by a single punk.