The reward for capturing the killers of an Iraq war veteran has long since doubled, but there are still no answers as to who gunned down Paul Zeller.

The 24-year-old had just stopped at a Harris Teeter in Pentagon City and was continuing his midnight walk home from work when he was shot at close range. Police have not yet developed a motive for the June 30, 2006, killing, though they say it’s not believed to have been a robbery.