Magistrates yesterday ordered the arrest of two men, Massimiliano Marchetti and Enrico Carella, both working for a small family firm hired to rewire La Fenice as part of a major restoration programme.
According to judicial sources, the Carella company was at least two months behind schedule and risked incurring heavy fines from the city council. The prosecution believes the company preferred to destroy La Fenice altogether rather than risk its own livelihood.
Prosecutors have suspected arson for some time, although until recently they were speculating that the fire might have been the work of an organised crime group. A number of basic safety rules had been violated, and none of the opera house's fire alarms or sprinklers managed to work once the fire began raging.
Marchetti and Carella told magistrates that they had left the building at 8.30 on the night of the fire, but other witnesses saw them leaving half an hour later.
That missing half-hour was crucial to the sequence of events, but according to the two men's lawyers the discrepancy was far from concrete evidence of their clients' guilt.
"The prosecution's case is one big logical hypothesis, with nothing solid behind it," one lawyer told reporters.
Fires have a nasty habit of breaking out in prestigious buildings in Italy just as restoration work is reaching its conclusion. Last month, the chapel containing the Turin Shroud was ravaged by flames at the end of a two-year restoration programme.
In 1991 the Petruzzelli theatre in Bari, in southern Italy, met a similar fate - an affair now believed to have been inspired by intrigues in the local worlds of politics and organised crime.