NEWARK, N.J. — U.S. Sen. Cory Booker is mourning the death of a former neighbor who was among four people killed in a series of shootings in New Jersey's largest city.

Two people were also wounded in the shootings that occurred Monday and Tuesday in Newark. Authorities say it doesn't appear that any of the shootings are connected, but motives for all four remain under investigation.

The first two occurred Monday when two men were shot and killed on city streets.

Booker said he knew one of the victims, 28-year-old Shahad Smith, of Bloomfield, who was his downstairs neighbor at the former Brick Towers housing complex. He said Smith's life mattered, so "his death must matter."

The other shootings occurred early Tuesday, when a man was killed in a street shooting and two other people were shot and wounded.