1. by attorney; 2.keypoint for OR:

evidence of national and international reputation
independent reference
my attorney did superb job on drafting and arranging letters, although I'm pretty good at English writing, I won't be able to draft the letters in such clear, and professional ways.
The petition letter is also very important, should be someone from your employer who knows your work so well and can describe it (at least convincingly). My petition letter was about 10 pages, written (at least signed) by my immediate supervisor, co-signed by department chair, and university. And it was written in the style that my petitioner (my boss) has already read all other supporting letters and used those as strong evidence (he cited those key points mentioned in other letters) that why I should be considered as an OR.