José Alonso Compeán is a former United States Border Patrol Agent, convicted of shooting an unarmed, illegal alien drug smuggler on the United States–Mexico border near El Paso, Texas, on February 17, 2005 and “obstructing justice by willfully defacing the crime scene”.
http://en.wikipedia.org/wiki/Jose_Compean
Regulations
General regulations regarding the submission, consideration and award of pardons are set down in Title 28 of the U.S. Code of Federal Regulations, Sections 1.1-1.10. The regulations suggest a five-year waiting period (after conviction or the end of incarceration) before a person becomes eligible to apply for a pardon,
http://jurist.law.pitt.edu/pardons3.htm