One of the letters was sent to Treasurer Mike Nahan’s electorate office.
WA Police spokesman Steve George said police responded to the discovery of two ‘suspicious’ items at the Australia Post mail processing site on Boud Avenue, Perth Airport, early Wednesday morning.
There was nothing elaborate about the letters, but they were deemed suspicious because of threatening words on them and a powder substance found within.
It took officers about 20-minutes to discover the powder was plain household flour, but as a precautionary measure, police blocked off roads in the immediate area.
It is understood police were first alerted to the issue when a machine accidentally opened one of the letters, addressed to WA Newspapers.
The second letter was addressed to an undisclosed government agency.
Shortly after, police received further calls to the electorate office of Treasurer Mike Nahan, at Riverton Forum Shopping Centre, as well as Premier Colin Barnett’s electoral office in Cottesloe.
It came after staff discovered two more similar letters filled with white powder.
‘Police further responded to these locations and again, as a precautionary measure, evacuated the immediate vicinity, until the items could be assessed,’ Mr George said.
The powder was again found to be harmless.
At a press conference on Thursday morning, State Crime Acting Commander Tony Flack said police had discovered a fifth package at Parliament House that morning addressed to Mr Barnett.
Mr Flack said police could establish a person of interest based on the letters’ recipients and said the offender could face two to 14 years jail time.
He said there was ‘nothing elaborate’ about the way the message was conveyed.
‘It’s not elaborate in the sense we’re dealing with a mastermind,’ Mr Flack said.
‘When you combine the players who receive it’