It's an office run for 19 years by the retiring Lynne Abraham.
If elected, both men are vowing to tackle illegal guns, considered the city's most serious crime problem. It's a complicated issue because state lawmakers have not allowed Philadelphia to establish its own tougher gun laws.
"My policy is very simple. It is no negotiated pleas in cases involving guns. An individual can plead guilty or have a trial," Untermayer said.
"The DA can set up wires, grand juries, use undercover sting operations to go after gun dealers like Colisimo's that sell guns illegally, and by going after people who sell guns to kids out of the trunks of cars," said Williams.
The 42 year old Williams is a former prosecutor and city inspector general.
At 58, Untermeyer is a lawyer and real-estate developer who was a registered Democrat until earlier this year.
Action News Anchor Jim Gardner asked the candidates how they will accomplish their crime-fighting goals given the city's current budget woes.
"I have to make do with what we have, but I also have to reach out to get grants from the federal government, from the state government, from the Pew Charitable trusts... To get money that we need for priorities," said Williams.
"What you need is a district attorney that's going to be creative. That's going to find funds from different services, different than we've used traditionally," said Untermayer.