PROSPECT, Maine — There’s something happening here. What it is ain’t exactly clear, to quote the song.

That’s why members of the Bangor Ghost Hunters Association spent the night recently at the Fort Knox historic site. Armed with video and still cameras, tape recorders, trifield meters and their own senses, a group of 17 investigators, including one staff member from the fort, set out on the night of Oct. 10 to explore the otherworldly side of the fort.

Members of the 8-year-old organization presented some preliminary evidence to fort officials Wednesday, and though much of it was inconclusive, they said they did have some unexplained experiences during their investigation.

“I’m not going to say it’s haunted,” said Harold Murray, director and lead investigator for the organization. “But something is going on here. There’s a lot of unexplained phenomena.”

The ghost hunters spent about seven hours at different locations in the fort. Most of the events they described Wednesday took place near the officers’ quarters, not far from the area where earlier this month a fort worker said he saw a shadowy form moving through the fort.

The group was taping in the officers’ quarters when, they said, a door opened by itself.

A group was sitting on the floor, and Murray was in a doorway with a hand-held video camera. Another filmer was at the other end of the room.

“I heard someone walking behind me; I thought it was the other camera guy,” Murray said. “But there was no one there. Then the door opens.”

The door was a latch-type door that opened to the fort’s inner court. It was a difficult latch to operate and, like many old doors, you had to push on the door before the latch would lift.

“I thought someone had just left,” Murray said.

The cameras in the room did not capture the door opening, nor did any of the outside cameras. The video did indicate, however, that no one came out of the officer’s quarters.

Meanwhile, the group on the floor had its own unexplained incident. The group — all women because there have been previous reports that there was a spirit in the fort who responded best to women — was seated on the wooden floor. Although no one was moving in the room, they felt vibrations.

“I felt the floor vibrating,” said Danielle Hopkins of Orland, a fort staff member who accompanied the investigation team. “It felt like someone was on the balls of their feet and jumping up and down or walking around the room. It wasn’t continuous. It would go for a couple of seconds and then stop. Then start again. We were there for about 20 minutes and it did it the whole time we were sitting on the floor.”

Murray, Hopkins and ghost hunter Kelly Moore of Howland tried Wednesday to recreate the effect in the room, but were not successful.

The team has a number of photographs that show “orbs” in them that were visible to the naked eye. Murray explained that the orbs in most of the photos were reflections from dust or moisture in the air when the photo was taken.

Two photographs, however, show a bright ball of light that appears to be moving, creating a spiral effect in the image. Because it appears to be moving, Murray said, they call it a “traveler.”

Murray offered two explanations for the orbs.

“It could be static electricity,” he said. “And our instruments showed that there was static electricity building up that night. Or it could be spirit energy. Some people think that’s how we make contact with the spirit world.”

During their investigation, Murray tried to invite spirits to contact them, first calling on Union soldiers and then challenging them, posing as a son of the Confederacy. In one instance, there was a response.

“It sounded like someone clearing their throat,” he said.

When they viewed the video-tape, the sound was different, a tapping, followed by a sharp rap, followed by soft tapping. Investigators offered several explanations of the sound: musket fire, cannon fire, a drum roll. But they have no explanation as to where the sound came from.

They also said there is a section of the video in which faint music can be heard, music that was not heard the night they spent in the fort. That music, which Murray described as sounding like a music box, was not audible on the video during Wednesday’s presentation.

Moore is one of the group’s photographers who documented the investigation. She said she experienced one of several equipment malfunctions the crew had during the night.

She had gone into the bakery area of the fort where there is a large oven.

“I tried to get a picture of the ovens,” she said. “The camera had been working fine. But when I tried to get a picture, it just stopped. Dead. Both cameras. I thought it was the batteries. But it worked fine when I went out.”

Ghost Hunter Association members are still going through the tapes from the visit to the fort and are not drawing too many conclusions at this time. Murray said he wants to come back to the fort, with a smaller crew to focus on just the area around the officer’s quarters.

“But I want to figure out what’s going on here,” he said.