The unnamed comic book store guy is the thief of murder victim Emily Sullivan's phone. When the phone was tracked, Benson and Stabler were about to arrest him on suspicion of murder when he was doing phone sex.
Confused, he denied the murder and said he'd pay for the calls. They released him, and he was eager they were investigating a murder and asked for details, but the detectives refused and he let it go. (SVU: "Mean")