The mother of Navy Yard gunman Aaron Alexis issued a statement expressing her sorrow and disbelief at her son’s shooting rampage on Monday.

Aaron’s mother, Cathleen Alexis, released an audio statement on MSNBC. She said, “I don’t know why he did what he did, and I’ll never be able to ask him why. Aaron is now in a place where he can no longer do harm to anyone, and for that I am glad.”

The 36-year-old man shot 12 people to death in the Washington Navy Yard on Monday. He was killed in a shootout with the police, according to CNN.

The victims ranged from age 46 to 73. They were all civilians who were starting their work day at the Navy Yard military compound.

Cathleen expressed her deepest sympathies to their families in her statement. She said, “To the families of the victims, I am so, so very sorry that this has happened. My heart is broken.”

Authorities are still investigating the motive behind the massacre.