Investigators seized documents on Wednesday from the headquarters of the Lombardy regional government, media reports said.
They were investigating the deaths of “around 180 people” at Milan's Pio Albergo Trivulzio care home since Italy's coronavirus outbreak erupted in February, the AGI news agency said.
The home's medical records were reportedly seized on Monday to determine whether staff negligence may have caused the virus to spread and kill the residents.
The Pio Albergo Trivulzio care home is one of Europe's largest, providing lodgings for several thousand people.
Italy's La Repubblica newspaper said the home was suspected of concealing numerous COVID-19 fatalities.
Italy has officially recorded 21,645 deaths from the virus – the world's second-highest total after the United States.
But most care-home deaths are not included in the official statistics and some doctors suspect Italy's real toll might be twice as high.