Authorities say the unidentified human remains were found on land in a densely wooded area of Prairie Park. They did not release any details about the cause of death Saturday night.
Authorities did not confirm that the remains were Keller's. Police were still gathering evidence at Prairie Park.
"Investigators are actively pursuing leads in the case and are seeking information about any suspicious activity or persons in Prairie Park on or about the time of Keller's disappearance," said Bill Feithen of the DeKalb County Major Case Squad.
Police established a hotline-- (815) 753-4NIU/ (815) 753-4648 -- in the case and are asking anyone who may have seen anything around the time of her disappearance to call. Phones will be answered from 9 a.m. to 6 p.m. Sunday.
Police said the remains were found in a densely wooded area, and that items believed to have belonged to Keller were discovered nearby. The investigators would not say if the remains showed signs of injury or trauma.
"The investigators are pursuing various leads," said Feithen. "We have kept them very busy to this point. So, it is very much an active investigation."
Keller, an 18-year-old NIU freshman from Plainfield, was last seen nine days ago, when she told friends she was planning to work on a school art project in the same park where the remains were discovered.
Investigators searched the area on the ground and from the air, and diving teams swept the Kishwaukee River.
"We continue to build on the information that we developed through the course of the investigation and the items of interest that we recovered," said Feithen. "It is an ongoing process that has brought us to this point."
The disappearance stunned the NIU community. Students had been passing out missing flyers and spreading the word on Facebook.
Counselors have been on campus trying to help people cope.
"Our counselors are actually going to the students, they're actually going to them and talking to them, they're talking to faculty, they're talking to university personnel," said NIU spokesman Brad Hoey. "This affects everybody."
In the wake of Keller's disappearance, NIU has added additional safety and security measures on campus.
The school is offering 24-hour security escorts for students and faculty that request them, and it has also added extra access restrictions at dormitories on campus.