I'm pretty sure I see the same aircraft or something similar at high altitude traveling the same direction, more north/south though, in the early evening , Thursday night was the last time .Most commercial jets seem from my vantage point {northern suburbs Perth} to travel a more east/west flight path.Next time I''ll have the binos and see if i can make out a tail colour.
The WA police force has a fixed wing aircraft called Polair62 that circuits the city to in conjunction with Polair61 {chopper}.If you have scanner you might be able to do some eavesdropping
http://warsug.info/index.php