A university dorm was among modern buildings which collapsed
An investigation has begun into allegations of poor building work which may have exacerbated damage caused by Monday's central Italian earthquake.
The chief prosecutor of quake-hit L'Aquila said standards must be checked after experts said more structures should have withstood the quake.
Rescuers are still searching the rubble for missing people.
At least one more body was pulled out on Saturday, raising the death toll from the 6.3 magnitude quake to 293.
On Friday, friends and relatives, along with senior Italian officials, attended a funeral service in L'Aquila for 205 victims, as the whole country held a day of mourning.
The government has said the search for survivors will end on Sunday.
But rescue workers believe the chances of finding anyone alive after the earthquake are remote and so are focusing on recovering bodies and assessing the damage.
Searchers picked through the rubble of one four-storey house in L'Aquila on Saturday after sniffer dogs picked up human scent, but no survivors have been found there.
L'Aquila prosecutor Alfredo Rossini refused to say which buildings were subject to investigation, but they are thought to include those built since stringent new seismic safety standards were introduced.
"We have the duty to verify whether some buildings were really constructed out of sand, as has been indicated from several sources, or in other cases without steel," La Repubblica newspaper quoted him as saying.
In a TV report on Friday, rescuers said that some reinforced concrete pillars appeared to have been made with sand.
The new construction rules were introduced following an earthquake in 1980 near Naples in which 2,500 people were killed.
L'Aquila's San Salvatore hospital and a university hall of residence in the town were both badly damaged in the earthquake despite being built since 1980.
Italian Prime Minister Silvio Berlusconi has said the first of a series of "new towns" for provincial capitals will be built in L'Aquila.