Is it possible that the last known Jaguar in the United States has been killed by a government employee? This could indeed be the case according to news reports out of the United States.
The Jaguar was caught in Arizona and released with a radio tag. However, the animal was soon found to be in poor health and was captured again and put down. It would seem that injuries sustained in the original capture of the Jaguar led to its death and the possible extinction of the Jaguar in the United States and certainly within Arizona. The capture of the Jaguar appears to have been in violation of the Endangered Species Act.
For more information see:
http://www.azstarnet.com/news/state-and-regional/article_c1fa70e7-ec29-50ee-8de2-015fcbd515e7.html
Kevin's Walk on the Wild Side 
A further article on the Jaguar in the United States:
http://www.nytimes.com/2010/01/25/opinion/25rabinowitz.html