NEW YORK (AP) -- The mother of the man who killed 12 people at the Washington Navy Yard said she is "so, so very sorry that this has happened."
Cathleen Alexis said Wednesday in New York City that she does not know why her son, Aaron, did what he did and she will never be able to ask him.
The mother read a statement at her home in Brooklyn. She concluded, "My heart is broken."
She did not want to appear on camera and did not take questions from a reporter.
Thirty-four-year-old Aaron Alexis opened fire at the Navy Yard on Monday before he was killed in a shootout with police.
Authorities said he had been suffering a host of serious mental problems including paranoia and a sleep disorder.
Meanwhile, the chief of the U.S. Capitol Police has ordered an investigation into the force's response to Monday's mass shooting.
Chief Kim Dine has asked the Capitol Police Board to conduct an independent review of the force's role in the aftermath of the shootings.
The fact review team is expected to probe reports that one of the force's tactical response teams arrived within minutes of the shootings and were told by a supervisor to stand down. The British Broadcasting Corp. and other news outlets reported that a Capitol Police watch commander issued the order.
Dine directed the review team to report its findings by October 21.
The Washington Navy Yard was scheduled to reopen and return to nearly normal operations at 6 a.m. on Thursday.
Navy spokeswoman Lt. Cmdr. Sarah Flaherty said Thursday will be a regular work day, except for Building 197 where the shootings occurred and the base gym. She also said the gym is being used as a staging area for the FBI to investigate Monday's rampage.