Authorities in Tennessee are offering a $50,000 reward -- up from $25,000 -- for information leading to the arrest of the suspects who gunned down two workers at a rural post office.

The perpetrators in Monday's deadly shooting in Henning, Tenn., remain at large, MyFoxMemphis.com reports, and officials have now increased their reward for any clues leading to an arrest and conviction in the case.

Killed were Judy Spray, 58, a rural carrier associate, and Paula Robinson, 33, a retail clerk. Their bodies were removed from the post office and sent to a medical examiner late Monday night for autopsies.

No arrests have been made and authorities have not yet determined a motive. 

More than 60 investigators from federal, state and local law enforcement agencies gathered evidence at the crime scene Tuesday and searched for the perpetrators who shot the women at the post office -- which doubles as a community center -- the station reports. 

Mike Dunavant, the Lauderdale County District Attorney, said Monday that the suspect or suspects were armed and dangerous and said the killings were done with "disturbing violence."

Spray and Robinson were well-known to residents who often come to pick up their mail at the post office, which sits between a self-service car wash and a coin-operated laundry called "Mom's" in this western Tennessee town of about 1,200 people.

Ella Holloway, who lives within walking distance, was accustomed to seeing Robinson's smile when she went to the post office to buy stamps. Another local woman said she knew Spray, describing her as being "nice as can be" when she delivered the mail.

"She's always smiling, when I think of her, I think about a big smile, a big laugh," Robinson's brother, Andre Croom, told MyFoxMemphis.com. 

Spray and Robinson were the only ones in the post office during the shooting, said Yulanda Burns, a spokeswoman for the U.S. postal inspection service.

Keith Morris, assistant inspector in charge of the U.S. Postal Inspection Service in Memphis, said officials have several possible motives. Authorities were urging the members of the public who may have information to contact investigators.

"We have a lot of theories that are in play at this point," he said.

Mary Hammock, who is a cook at the gas station within sight of the post office, said she had been in the post office about 8:25 a.m. Monday and noticed it was not as loud or busy as normal.

"I knew something didn't feel right because it was real quiet," she said. She returned to the gas station and heard police sirens about 15 minutes later.

"I might have been real close probably to losing my life," she said.

Gassing up his red pickup truck at the gas station Tuesday, farmer George Arender said residents are speculating on a motive, from robbery to a drug package delivery gone bad.

"They're devastated," Arender said. "They just can't figure out a motive for this."

Read more on this story from MyFoxMemphis.com

The Associated Press contributed to this report