LAKEWOOD, Wash. -- Police investigating the death of Adre'anna Jackson said they have recovered enough evidence at the vacant lot where the 10-year-old's remains were found that they are confident it will lead to her killer.

Lakewood police would not give specifics about what they have uncovered, but detectives and FBI agents have scoured the lot in one of the largest crime scene searches in Pierce County history.

Meanwhile, police continued to look for a transient man they think may have information that would help their investigation.

Video: Girlfriend Of 'Potential Witness' Talks To KIRO 7

Police Chief Larry Saunders said Spencer Douglas Grant, 44, is apparently familiar with the area where the bones were found.

Grant's girlfriend spoke to KIRO 7 Eyewitness News about what Grant found, "He wanted me to go look at the skull and see if I thought it might be her."

"Underneath this pine tree there was a back pack and clothes kind of scattered in the branches underneath about her size," said Grant's girlfriend.

Grant was in jail at the time Jackson disappeared in December, but officials said he was known to frequent the undeveloped lot.

The FBI on Monday added $50,000 to the reward for information about the case.

People with information can contact Lakewood police or CrimeStoppers at 253-591-5959.

Free crisis counseling for students and families of Tillicum Elementary School is available through Greater Lakes Mental Health Care 253-581-7020.