US prosecutors have called dozens of hospital staff to give evidence over claims of a euthanasia policy in dealing with Hurricane Katrina victims.
Hospital officials said there were problems with its evacuation
A total of 73 staff at New Orleans' Memorial Hospital were issued with the subpoenas, a spokeswoman for Louisiana's attorney general said.
Those called include doctors, nurses, and support staff.
A spokesman for Tenet Healthcare Corporation, the hospital's owner, said it was co-operating with investigators.
Previously, Tenet said that 34 patients had died after the hospital was cut off by flood waters, and 24 of those had been in a facility on the hospital grounds run by a separate company.
In all, more than 970 people are known to have died in the city and the surrounding state of Louisiana, and more than 200 in neighbouring Mississippi.
Louisiana attorney general's office said on Tuesday it was investigating the deaths of more than 200 people in total at nursing homes and hospitals during and after the hurricane.
Allegations range from negligence to euthanasia, spokeswoman Kris Wartelle told Reuters news agency, adding that many were likely to be unsubstantiated.
However, on Wednesday prosecutors issued the 73 summonses "for all levels of personnel" at Memorial Hospital.
"All we can say is that we had to issue the subpoenas to get those people to talk to us," Ms Wartelle said.
Two weeks ago Tenet's assistant general counsel, Audrey Andrews, sent out a memo detailing the legal rights of staff and pointing out that employees could decide whether or not they wanted to be interviewed.
The Memorial Hospital denied any attempt to dissuade people from coming forward.
"We have never discouraged any employee from working with the Louisiana attorney-general's office," CNN quoted a spokesman as saying.
Two nursing home owners were charged with manslaughter in September over the deaths of 34 people at St Rita's home.
Mable Mangano and Salvador Mangano Sr were accused of ignoring mandatory orders to evacuate residents.