Photograph: Victor J. Blue (Victor J. Blue)

The U.S. Postal Service Inspector General’s office said Wednesday that it is launching an investigation into the shift in mail delivery to evening hours, a change that’s alarmed letter carriers and customers.

The probe by the Postal Service watchdog comes less than a week after a carrier was fatally shot in suburban Maryland as he was delivering the mail. The killing last Saturday of  Tyson Jerome Barnette, a part-time carrier who relieved full-time carriers of excess workloads, has focused attention on the increasingly late hours that mail is delivered and why. Barnette was shot in Prince George’s County about 7:30 p.m.

Agapi Doulaveris, spokeswoman for Inspector General David Williams, said the audit should take several months.

The inspector general reported in July that the Postal Service’s use of overtime has soared since the number of letter carriers has shrunk with declining mail volume.