The administrator opened the package but was not injured by the corrosive liquid it contained, Lissl said.
Lissl said a preliminary investigation suggested all four packages contained butyric acid - a corrosive substance that is harmful if swallowed or inhaled and is considered a severe skin, eye and respiratory irritant.
On Friday, an official in the town of Weisskirchen was treated at a hospital for burns to both hands and a thigh after he opened a package at his home office. Police said they intercepted two similar packages sent to other officials in the town about 120 miles west of Vienna.
All four packages were mailed from Passau, Germany, just over the border from the western Austrian city of Linz, Lissl said Saturday.
Federal counterterrorism officials took charge of the investigation, Austrian media reported Saturday, and experts with the Federal Criminal Investigations Bureau - Austria's equivalent of the FBI - were examining the packages for DNA and fingerprints.
Results from forensics tests being conducted in Salzburg were not expected until sometime next week.
Investigators said they could not be certain the same individual sent all four packages, though police said they were working on the assumption that whoever mailed them held a grudge.
Officials said the exact motive remained unclear. The official who suffered the burns - former Weisskirchen mayor Rudolf Prinz - is a member of the ruling Social Democratic Party, yet two of the other packages targeted officials with the conservative Austrian People's Party.
The acid sent to Prinz was hidden in a cigar box, Lissl said. Locals said that suggested the sender is an acquaintance.
"Only insiders know how much Mr. Prinz enjoys a good cigar," the Austria Press Agency quoted Weisskirchen resident Irmgard Balasch as saying.
Prinz, 61, said he was injured when he opened the package and it released a noxious vapor. In addition to the burns, he was treated for an inflamed eye and inflamed nasal passages.
"It burned my eyes, my nose and my skin, and it stank up the whole house," Prinz told Austrian public broadcaster ORF.
Prinz was quoted by the newspaper Oberoesterreichischen Nachrichten as saying he had received threats in 2000 after the municipality refused to allow developers to build on a valuable plot of land.
Authorities declined to comment on whether those threats were linked to Friday's acid attack.