U.S. Sen. Lisa Murkowski says she's not satisfied with the explanation she received on the government's handling of a key witness in an Alaska corruption case.

Murkowski requested an inquiry into the Justice Department's investigation and decision not to prosecute Bill Allen on charges of transporting a minor across state lines for immoral or exploitative purposes.

In a letter to Murkowski, Assistant Attorney General Ronald Weich said Justice officials have wide discretion in deciding whether to pursue criminal charges. He said Justice's internal ethics watchdog, charged with determining whether the decision not to prosecute Allen was based on improper factors, found further investigation of the matter unwarranted.

Allen was a key witness in an investigation that ensnared then-Sen. Ted Stevens. Stevens' conviction was tossed after the Justice Department admitted misconduct.