(ABC NEWS) -- A group of Ohio State University college students were shocked to find that their off-campus house came with an additional roommate, a mysterious man named "Jeremy" who had been living in the basement without their knowledge.
"It could have potentially been a scary situation," Mark Hartman, 21, told ABCNews.com. "Two of the 10 roommates in our section of the house are girls and our rooms don't have locks on the doors."
Hartman, a senior at Ohio State, said his group of friends moved in Aug. 5, when their lease began and they started encountering a number of problems with the house on 13th Avenue in Columbus, Ohio. For one thing, the power would go off continuously on the third floor and someone would have to go to the basement to flip the circuit breaker.
"A few times, when my roommate Brett was down there, he would hear noises," Hartman said. "But, when he tried to turn the handle on a door located in the basement, it was always locked."
One time, Brett saw a person in the basement and asked him if he lived in the house, he added.
"The guy said his name was Jeremy but wouldn't answer Brett's questions and just walked out of the house," Hartman said.
As the weeks went on, the roommates started noticing strange things happening around the house, he said. Drawers would be left open in the kitchen and bathroom, lights turned on, and those noises from the basement continued.
Hartman admitted it all had some of his housemates thinking the place was haunted.
The roommates did a thorough check of the house, according to Hartman, but decided to call the landlord and eventually the police when they were unable to open that locked basement door.
"The landlord and police pried off the door handle and, inside, we found a livable bedroom with photos, a TV and clothes," Hartman said.
That's when the roommates connected the dots and realized that "Jeremy" had been living in the basement for an extended period of time without paying rent. He used a side door to enter the basement, never seen by the other members of the house.
The housemates were upset that NorthSteppe Realty evidently had missed someone squatting in the house, with access to all of their belongings.
NorthSteppe did not immediately respond to ABCNews.com's request for comment.
Jeremy turned out not to be a "bad guy" Hartman said, though he said he shouldn't have been allowed to live in the house and has since moved out.
The rental company immediately changed the locks, but Hartman said that's not enough. He's considering taking legal action against NorthSteppe, one of the larger property managers in Columbus.
"We are hoping for discounted rent for a few months," he said. "We've talked to student legal services."
The civil engineering student adds that once the additional roommate was identified, suddenly the realtor started fixing things around the house.