(AP) — Gov. Dave Heineman says all U.S. and state flags in Nebraska will be flown at half-staff in honor of the victims of the Washington Navy Yard shooting.

Flags will be flown at half-staff until sunset on Sept. 20. Heineman made the announcement in accordance with a proclamation from President Barack Obama.

A former Navy man opened fire Monday morning inside a building at the heavily secured Washington Navy Yard. Thirteen people were killed, including the gunman.