"To see them digging in a building so close to where he disappeared was shocking," Ann Collins said.
The search Tuesday of a backyard and garage of a home near the city's Haight-Ashbury district has renewed interest in the high-profile disappearance in 1984. Photographs of the freckled-face boy, plastered on milk cartons and posters throughout San Francisco, turned it into one of the first child disappearances to garner national attention.
The home search was a "follow up to the cold case investigation," police said in a statement.
A law enforcement official, speaking on condition of anonymity because the search warrant was sealed, said a "person of interest" in the disappearance lived in the house at the time. That person has since died, and police said the current residents were not suspects.
Police didn't disclose what prompted investigators to seek a search warrant and renew the probe into the case. The FBI and the Alameda County sheriff's department contributed to the search.
During the search, cadaver dogs indicated remains were under the concrete in the garage. Police said a preliminary review showed them to be animal bones, but the San Francisco medical examiner's office was conducting tests.
Collins, Kevin's mother, said she felt mostly "just numb" as the search took her on an emotional roller coaster ride, especially after the remains were reported to be from an animal.
Since her son's disappearance, Collins and her husband divorced, and she moved to the San Francisco suburb of Concord.
"It would be nice to have closure," she said. "But then a part of me, you know, doesn't want to find him like that."
Kevin was last seen waiting for a bus after basketball practice at St. Agnes School in the Haight. The search for him went citywide, and his photograph was on the cover of Newsweek in 1984.