Outgoing Montgomery County District Attorney Bruce Castor will join the Blue Bell-based law firm of Elliott Greenleaf & Siedzikowski in January, it was announced yesterday.

Castor, who was elected in November to be a Montgomery County commissioner, said that while "locking up criminals is really fun," it was time for him to do something different.

"One of the areas the firm is interested in having me do is the internal investigation of corporations," Castor said. This would include helping clients deal with regulatory problems or prepare for audits, he said.

The firm employs about 40 attorneys and handles cases involving business, contracts, the environment, federal civil rights litigation, health care, bankruptcy, taxes, white-collar criminals, RICO law and grand juries. State Sen. Stuart J. Greenleaf (R., Montgomery) and former State Rep. Melissa Murphy Weber are with the practice. The late Gov. Robert P. Casey was an attorney for the firm.

On the same day he joins the firm, Jan. 7, Castor will officially start as commissioner.

He said he was now meeting with the county's department heads and "tying up loose ends" on criminal cases.

Castor has been a prosecutor since 1986 and served six years as first assistant before being elected to two terms as district attorney.

He is president of the Pennsylvania District Attorneys Association.

Contact staff writer Mari A. Schaefer at 610-892-9149 or mschaefer@phillynews.com.