Prominent defense attorney Tariq El-Shabazz, who has represented some of the city's most notorious criminals, will join the District Attorney's Office next month as one of Seth Williams' top lieutenants, Williams announced Thursday.

El-Shabazz will be named deputy in charge of investigations in September and in December will become Williams' highest-ranking deputy when current first assistant George Mosee retires, Williams said at a news conference.

Williams described El-Shabazz as "an unmatched advocate" for developing relationships between the public and law enforcement, and said he looked forward to adding El-Shabazz's perspective to his senior staff.

"He will make a great deputy, and when the time comes he will make an outstanding first assistant," Williams said.

El-Shabazz, 52, a charismatic litigator, has known Williams for decades. He worked in the District Attorney's Office from 1988 to 1993 and recruited Williams to work there.

The two have remained friends, and they generated headlines when they sparred at a charity boxing match April 30 in North Philadelphia - won by El-Shabazz in a judges' decision.

After leaving the District Attorney's Office, El-Shabazz became one of the city's most visible defense attorneys. His client list at various times included drug kingpin Kaboni Savage; influential Muslim leader Imam Shamsud-din Ali, who later was convicted of corruption charges; and Kenneth Burno, convicted in 2004 of persuading his girlfriend, the so-called Black Widow, to shoot her ex-boyfriends.

El-Shabazz said he decided to rejoin the District Attorney's Office after being courted in recent weeks by Williams, who was looking to fill a vacancy atop his 42-employee Special Investigations Unit.

El-Shabazz also said he believed he could help strengthen the office's bonds with the community, not simply put criminals behind bars.

Mosee, who has been in the District Attorney's Office for nearly three decades, will work with El-Shabazz to prepare him to become Williams' right-hand man. Mosee is set to leave the office Dec. 9 after entering the city's controversial DROP retirement program.

El-Shabazz said that despite sparring with prosecutors in court for 23 years, he is eager to begin his new role on the other side of the law.

"When you stand for justice and you stand for right, there's no transition," El-Shabazz said. "There's no 'us against them'; there's just justice and there's right and wrong."

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Staff writer Chris Brennan contributed to this article.