An unsigned note reportedly left at the memorial marking the place where Ahmaud Arbery was killed is raising questions about who left it there and why.

The message, a photo of which was obtained by CNN affiliate WJXT, reads: “Ahmaud – I am so sorry. I should have stopped them. I am so sorry.”

S. Lee Merritt, the attorney for the Arbery family, addressed the note in a tweet, writing, “We need to discover who left this note!”

Arbery, a black man, was shot dead while jogging just outside Brunswick, Georgia, on February 23. The story hit the national spotlight this month after footage of the killing was released.

Two men, Gregory McMichael, 64, and his son, Travis McMichael, 34, were arrested Thursday in connection to Arbery’s killing. They face charges of felony murder and aggravated assault, according to the Georgia Bureau of Investigation.