“We’re still dealing with this stuff ourselves,” Lieutenant Lindsly said.

Mounds of waterlogged evidence bags continue to cause headaches in New Orleans more than seven years after Hurricane Katrina, pointing to the difficulty of preserving DNA evidence after flooding.

“If you don’t keep it properly stored, you’re affecting somebody’s life,” said Robbie Keen, who directs a federally financed DNA project in New Orleans that is still trying to recover evidence.

Ms. Keen said some of the damaged biological evidence from Hurricane Katrina had been successfully tested, but some had been lost.

The New York Police Department has assigned 20 officers, 6 civilians and a captain to recover evidence at the two warehouses, under the supervision of Robert S. Martinez, director of the department’s Support Services Bureau, Mr. Browne said. The department may also hire a private contractor to help with the cleanup of damaged documents, as New Orleans did.

Mr. Browne said an occupational safety team within the Police Department determined that the two warehouses had been contaminated, with substances including raw sewage, and that they had to be closed to workers. It was not clear when they would be safe to enter.

Longstanding problems in the vast police storage system have compounded the storm’s effects.

While the department now puts bar codes on evidence, it relied on paper records until a few years ago. The antiquated system still provides the only way to track millions of items in the department’s 11 storage areas.

“It was all piles — piles, piles, piles,” said John W. Cassidy, a retired officer who spent more than a decade in the property division. “It’s not like it was organized. You could have 50 vouchers on one pile.”