At least two of the 11 Los Angeles County Sheriff's Department employees caught up in a massive credit card fraud scheme are also suspected of having sold black tar heroin inside the Twin Towers Jail, sheriff's investigators told The Times on Thursday.

As a result of their suspicions, investigators brought trained dogs to the jail Wednesday as deputies searched employees' lockers. The department carried out 21 search warrants Wednesday, mostly at the homes of four deputies and seven civilian employees suspected of participating in two massive credit card fraud scams.

While [Sheriff Lee] Baca did not address the drug allegations, other sheriff's officials said they believe a deputy and custody assistant--a civilian employee in Twin Towers--were involved in selling heroin to inmates. Those allegations surfaced in the course of an undercover credit card sting operation the department's Internal Criminal Investigations Bureau conducted over the past seven months.