Probation officers searched the residence of James Claiborne in the 7600 block of Del Rosa Avenue.
Claiborne, 34, was released from state prison to probation supervision, after a felony conviction for evading officers in a vehicle.
"We were notified that Claiborne was in possession of a firearm," said San Bernardino County probation spokesman Chris Condon. "During the search we discovered the gun had been reported stolen."
Probation officials said they are continuing the investigation to find out if the gun had been used in any crimes.
The firearm reportedly was loaded when Claiborne was arrested.
In a separate investigation, probation officers said they discovered two probationers and two Post Release Community Supervision, or PRCS, offenders, with unrelated cases, all reportedly living at the same residence in the 2300 block of Kern Street.
It's a violation of terms of release for PRCS offenders or probationers to associate with each other or any felon, Condon said.
Probation officers said they discovered 20 people living on the property, including the four they were looking for.
Of the 20, nine were arrested, including a fugitive parolee, a PRCS offender with a no-bail warrant, two persons on susicion of drug-related offenses, and five with outstanding warrants.
A study released on Jan. 22 by the Council of State Governments found that statewide, probationers and parolees represent 22 percent of all persons arrested.
Chief Probation Officer Michelle Scray Brown referenced this report when commenting about the arrests.
"The Council of State Governments report clearly indicates that probation supervision reduces re-offense," she said. "Most supervised offenders change their behavior. However, those that do not are subject to arrest by probation officers who will investigate alleged violations of the law or probation terms."
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