Thieves caused more than $100,000 in damage and lost materials when they stripped cabling from the railway line near Sandown Park station on 1 March, police say.
Police remain on the hunt for the vandals, who broke into a Metro Trains control box near the station.
They then cut and stole fibre optic cable and copper cable, police say.
According to Metro Trains, almost 400 cables for signalling and other communications equipment were cut during the 1am attack.
It caused major disruptions on the Cranbourne and Pakenham lines for most of the day.
Buses replaced trains for parts of the lines during the morning and afternoon peaks, with delays of up to 60 minutes.
Metro Trains chief executive Raymond O’Flaherty labelled it a “senseless act of vandalism”.
“I was taken aback by the extent of this brazen attack on our rail system.”
Any information to Crime Stoppers on 1800 333 000.
