Trayvon Martin

Updated 6:15 p.m. ET

George Zimmerman, who fatally shot unarmed black teenager Trayvon Martin in 2012 and was acquitted of all charges in the case, said Thursday that he was auctioning off the gun that he says he used in that incident.

Martin Family Photos via AP Photos

Hundreds of people are expected to gather at the federal courthouse in downtown Seattle Saturday as part of a Justice for Trayvon Martin National Day of Action.

The noon vigil will include Martin's cousin, Cedric Martin of Tacoma. It's being held as part of the Rev. Al Sharpton's nationwide Justice for Trayvon Martin Day, which is expected to include 100 cities across the country.