The Utah man -- accused of making a bomb threat, against the Salt Lake City Marathon -- has sent a letter of apology to organizers.

However, terrorist threat charges remain in place, against George Zinn, 59, of Salt Lake.

Police claim Zinn sent an email -- to members of the marathon's marketing department -- asking for help in planting bombs at the finish line.

The email was allegedly sent, just days after the Boston Marathon bombings.

Zinn claims the email was a "joke."