Officers with the aid of local villagers in Morobe province arrested the man on Sunday.
Five men were arrested in connection with the attack last week.
Provincial Police Commander Superintendent Leo Lamei said detectives were interrogating the suspects.
He said another three, including two brothers are still hiding in between the Salamaua coastlines and Wau jungles.
"We are tracking the three remaining suspects through the villages in and around Wau such as Bito, Skin Diwai, Biawen and Banis Donkey," he said in a statement on Sunday.
"Two suspects have surrounded to village leaders at Mubo and Salamaua respectively and have been air-lifted to Lae and are being interrogated," Supt Lamei said.
A total of six suspects are now in police custody.
Two of the three suspects are brothers who escaped from the Wau police cells in 2011.
"I thank the leaders and people for helping police capture the suspects. I appeal to them to continue assisting police capture the other remaining suspects," Supt Lamei said.