A 21-year-old Utah man indicted last week on gun and hate crime charges in a synagogue attack is a prolific participant in online white supremacist forums.

A federal grand jury indicted Macon Michael Openshaw on Wednesday with intentionally shooting at Congregation Kol Ami Synagogue in Salt Lake City sometime between Jan. 1, 2012, and April 30, 2012.

The indictment accuses Openshaw of firing several rounds at the synagogue, breaking windows and causing other damage in a crime that federal prosecutors say was motivated by hatred.

Openshaw was also charged with using a gun to commit a crime and possessing a firearm with an altered serial number and while subject to restraining orders filed by at least two people against him in the previous year.

The Anti-Defamation League reported that Openshaw claimed membership in a racist skinhead group in Salt Lake City and claimed allegiance to the now-defunct Vinland Folk Patriots, a white supremacist group.

Openshaw also frequently posted on the white supremacist Stormfront forum and used the numeric symbols 14 and 88, each of which holds special significance to white supremacists and neo-Nazis, and other racist iconography, the civil rights group says.

The group says Openshaw also subscribed to numerous white supremacist videos on YouTube and participated in the white supremacist social networking website Newsaxon, where he praised the Aryan Brotherhood’s use of violence.

Openshaw was convicted in 2011 of a misdemeanor weapons charge after police said he pulled a knife on a man using a cell phone in a movie theater, and he pleaded guilty last year to throwing his 65-year-old grandmother to the ground, slapping her and taking her phone to prevent her from calling for help.

[Skinhead white supremacist via Flickr]