Hound

From publisher blurb:

Meet the Hound, a U.S. Marine who had been MIA for three years. Upon his return, he was a changed man - stronger, faster, and with dog-like super keen senses. Due to his inability to recall the time he was missing, the Corps was unwilling to return him to active duty. There were other agencies more than willing to give him a job, though. Now the Hound acts as a federal agent specializing in investigating and tracking down other super humans. His access to experimental weaponry and devices means once the Hound has your scent, you're going down!