Postal unions are concerned that fewer full-time mail carriers and mail-sorting facilities means more letter carriers out after dark in unsafe conditions.

Those worries have grown with the shooting death of a carrier on his route in Prince George's County after sundown Nov. 23.

Twenty-six-year-old Tyson Barnette of Upper Marlboro was gunned down on the job about 7:20 p.m. in Cheverly.

Prince George's police and U.S. postal inspectors have released few details. They have identified no suspect and no motive. They would not say last week whether Barnette had been robbed of mail or personal possessions.

Postal Inspector Frank Schissler said investigators are "exploring all possible angles."

"Robbery is, of course, one of those possibilities," he said, "but it's not the only thing we're focusing on."

Union leaders suspect the time of the evening might have been a factor. They have raised concerns about the hours that carriers are required to work — especially at this time of year, when the Postal Service's heaviest volume coincides with the shortest days.

The National Association of Letter Carriers, which represented Barnette but did not count him as a member, said it is not blaming Postal Service policies for his death. But Jim Sauder, chief of staff to association president Fred Rolando, said a trend toward later hours raises concerns.

Sauder said mail delivery has always involved work after dark, but he said reports of carriers still on the street at 9 p.m. are worrisome.

"It can be unsafe to deliver in certain parts of the country after dark," Sauder said. It isn't just a matter of crime, he said, but accidents that occur as a result of low light.

Sauder said a joint labor-management task force is looking into the question of late hours.

Mark Diamondstein, president of the American Postal Workers Union, said plant consolidations and workforce cutbacks have contributed to unsafe conditions.

"Mail now arrives at carrier stations later, pushing delivery times into the evening, and stations are understaffed," Diamondstein said.

The Postal Service says most of its mail delivery occurs between 9 a.m. and 5 p.m.

"While the USPS strives to have carriers off the street by 5 or 6 p.m. there are occasions when this is not feasible," spokeswoman Agapi Doulaveris said in a written response to questions from The Baltimore Sun.

Nevertheless, the Postal Service's inspector general has launched an investigation of deliveries after 5 p.m. She said the audit could take months.

The Postal Service posted a $5 billion loss for the last federal budget year, despite a nearly $1 billion increase in revenue. Its parcel services continued their steady growth while the volume of first-class mail continued its steady, Internet-related decline.

Part of the Postal Service's problem is that even as it has shed full-time employees, its overtime costs have soared over the past four years to more than $3.5 billion annually, according to the inspector general. One key reason was that carriers were hitting the streets late because of delays in getting their mail, forcing them to work longer into the evening.

Barnette was what is known as a "city carrier assistant," a noncareer worker who delivers mail in urban and denser suburban areas at an average starting wage of $15 an hour.

The Postal Service says such workers make up an increasing percentage of its workforce, while 200,000 career carriers — who make an average starting salary of $22 an hour — have left the payroll over the past seven years.