BOSTON, MA - The state's prison commissioner is back on the witness stand today, testifying in a federal lawsuit filed by a convicted murderer who wants a sex-change operation.

Kathleen Dennehy said that allowing Robert Kosilek to complete his transformation into a woman would create "insurmountable" security problems in the prison system.

Dennehy said if Kosilek had the operation and was allowed to remain in an all-male prison, officials would be concerned about potential sexual assaults by male inmates. If Kosilek were sent to the all-female prison in Framingham, the commissioner said there would be other concerns for her safety.

Dennehy said Kosilek would have to be kept in a special housing unit, in almost total isolation. Kosilek is serving a life sentence for murdering his wife, Cheryl, in 1990.