Here's a story with more info.

http://www.nj.com/gloucester-county/index.ssf/2013/06/nascar_driver_jason_lefflers_fatal_crash_being_investigated_by_nj_state_police.html

Seems like he was racing alone in second place when he crashed into the 4th turn wall. Steering failure perhaps?

Loved watching Jason wheel a Silver Crown car at Phoenix. RIP Jason....