State investigators revealed yesterday the origin of the ferocious northern snakehead fish that have turned a muddy Crofton pond into a site of alien infestation: They came from New York.

A Maryland man brought two of the sharp-toothed, torpedo-shaped snakeheads home from New York to keep as pets. That he did, until the exotic predators outgrew his home aquarium and he dumped them into the Crofton pond, officials said.

He thought it would be safe for them there. He didn't realize that nothing else would be safe from them. Those two fish have probably spawned hundreds of babies, because biologists caught 99 juvenile snakeheads in the pond yesterday using electroshock gear.

"This person did something they thought was an innocent act," said Capt. Mark Sanders of the Maryland Natural Resources Police at a news conference where a 2-inch-long baby snakehead swam in a white basin under the glare of nine TV cameras.

"The individual had no idea it would create the situation we have today," Sanders said.

State officials expect to find many more of the fish, a native of China that can grow to 3 feet, survive for three days out of water and walk on land using its extended fins. It's scary in the water, too, devouring almost everything it meets.

Drastic measures will probably be needed to wipe out the snakeheads and protect nearby waterways, officials warn. The Little Patuxent River is 75 yards from the pond.

The state is assembling an expert panel that by the end of this month will recommend a plan while the DNR tries out various trapping methods.

"We could very easily be talking about hundreds, if not more, juvenile fish in the pond," said Eric C. Schwaab, DNR fisheries service director. But he added, "We have no reason to believe the fish have gone beyond the pond."

Authorities became aware of the fish in May, when a local angler caught an 18-inch snakehead and threw it back but took a photo to the DNR. Now department police have set up round-the-clock surveillance of the pond.

"We don't want the fish to go anywhere," said a determined Darrell Ford, a police officer guarding the pond yesterday. He had turned away more than 50 volunteer fish-hunters by midafternoon.

Officials would not release the name of the man who dumped the fish. Natural Resources Secretary J. Charles Fox said he wanted to spare the man from news media attention and perhaps physical harm. He could have faced a misdemeanor charge of releasing a nonindigenous species into the wild, but he will not be charged because the two-year statute of limitations has expired.

Police found the man last week after an investigation that began in late June and involved speaking with pond regulars and people who live and work nearby.

"We did receive tips that led us to a general area," Sanders said. "We were able to speak with an individual who openly admitted [releasing the fish] and expressed remorse."

He said the man is a Maryland resident who is familiar with the pond. The man had the fish for about two years before he decided to release them, Sanders said. They were 12 to 14 inches long at that time.

"They became unwanted pests to the individual, and [he] felt a need to dispose of them in a safe place," he said.

While that investigation has concluded, the state is just beginning to figure out what to do about the menacing fish. A 10-member expert panel will be headed by Donald Boesch, president of the University of Maryland Center for Environmental Sciences. The panel will recommend a course of action by the end of the month.

Options include poisoning the pond, draining it, treating it with chlorine, trapping and netting the snakeheads, or electroshocking the water and stunning the fish so they float to the surface.

"The good news is that if this is isolated to this one pond, there are a number of viable options that would be effective and not injurious to other resources in the long run," Boesch said.