Prosecutors say a 62-year-old man accused of a double homicide at a Coast Guard communications station is the only possible killer in a circumstantial case, countering defense arguments that the government hasn't proven guilt beyond a reasonable doubt.

The two sides in James Wells' federal murder trial presented their closing arguments Thursday in federal court in Anchorage, returning to themes well-established in weeks of testimony.

Wells is charged with two counts of first-degree murder in the shooting deaths of his co-workers, 41-year-old Petty Officer 1st Class James Hopkins and 51-year-old civilian supervisor Richard Belisle in April 2012 on Kodiak Island.

Prosecutors say Wells, a civilian, was unhappy that he was increasingly irrelevant on the job through the advancement of the victims.

Defense attorneys say authorities immediately zeroed in on Wells and ignored other suspects.