(CNN) -- Investigators are trying to determine whether a sweatshirt that volunteer searchers found Sunday is that of a missing California boy with cerebral palsy, Oakland police said.
Hasanni Campbell was last seen August 10 outside a shoe store in Oakland, California, his foster parents say.
Volunteers looking for 5-year-old Hasanni Campbell found a small gray sweatshirt partially buried Sunday afternoon off a cul-de-sac near an Oakland neighborhood where his foster parents reported he had disappeared last month, CNN affiliate KTVU reported, citing Oakland police.
Hasanni was said to have been wearing a gray sweatshirt on August 10, the day his foster father reported him missing, CNN affiliate KGO reported.
"Because [the sweatshirt found Sunday] is similar, it's gray, it does appear to be small ... and this is pretty close to the area where he was missing, we want to make sure that we analyze it and confirm," Oakland police Sgt. Arturo Bautista told reporters at the discovery site Sunday. Watch searchers pray after finding shirt »
Hasanni's foster parents, Louis Ross and Jennifer Campbell, told police Hasanni disappeared while Ross was dropping him off at a shoe store where Campbell worked.
Less than a month later, Oakland police said they were treating the disappearance as a homicide, and arrested Ross and Campbell -- who also is Hasanni's biological aunt -- on Aug. 28 as suspects. However, both were released a few days later after the Alameda County District Attorney's Office concluded there was insufficient evidence to charge them, Deputy District Attorney Tom Rogers said on September 1.
Police haven't said why the case had become a homicide investigation. A body has not been found.
Ross and Campbell, who are engaged, have maintained their innocence.
In an interview last month with HLN's Nancy Grace, Ross said he left Hasanni outside his BMW for two to five minutes while he went to get his fiancee to open the back door of the store.
"By the time I got there, Jennifer is already out of the store, walking toward me, asking, 'Where is Hasanni?' And I say, 'What do you mean, where is Hasanni?' And I look around to the side, and he is no longer there."
CNN's Emanuella Grinberg contributed to this report.