(CNN) -- The U.S. Postal Inspection Service on Tuesday doubled to $50,000 the reward it is offering for information leading to the arrest and conviction of whoever fatally shot two female postal employees Monday at the post office in western Tennessee, about 50 miles northeast of Memphis, Tennessee.
The service identified the victims as retail clerk Paula Robinson, 33, and rural carrier associate Judy Spray, 59. The shootings occurred at the post office in Henning, Tennessee, between 8:30 a.m. and 9 a.m.
The case is being jointly investigated by the U.S. Postal Inspection Service; the Bureau of Alcohol, Tobacco, Firearms, and Explosives; the FBI; the 25th Judicial District Attorney General's Office; the Tennessee Bureau of Investigation; the Tennessee Highway Patrol; the Lauderdale County Sheriff's Office; the Tipton County Sheriff's Office; and the Henning Police Department.
"This is a multi-agency response and investigation so that we are sure to be thorough and so that we can, as quickly as possible, determine who is responsible for this violence and bring those people to justice," District Attorney Mike Dunavant told reporters Tuesday.
More than 60 law enforcement officers nationwide have been assigned to the case, the service said. "Homicides in the Postal Service are rare, but when do they occur, make no mistake, we will aggressively investigate to find those responsible," said Inspector in Charge Martin D. Phanco of the U.S. Postal Inspection Service's division in Atlanta, Georgia.
The Memphis Commercial Appeal, without citing sources, said the shootings happened during an apparent robbery attempt at the post office, though neither Dunavant nor a representative of the postal inspection service would confirm that on Monday.