"Our heartfelt thoughts and prayers go out to the people affected by this tragic event. Please know that we are committed to working with the City of Philadelphia and other authorities to determine what happened yesterday."
Philadelphia assistant district attorneys Jennifer Selber and Edward Cameron and district attorney spokeswoman Tasha Jamerson toured the site Thursday.
Cameron specializes in prosecuting people accused of homicides for the city and is well-known nationally for prosecuting abortion doctor Kermit Gosnell.
CNN asked Jamerson why they were looking at the site.
"It's way too early to be discussing any aspects of the building collapse," she answered. "We took a tour of the scene just like the mayor's office took a tour and the police took a tour. Along with the rest of the city, the entire DA's office is thinking about and praying for the victims of yesterday's tragedy."
Crime scene units also toured the site.
Some saw it coming
People who work in the area had grown concerned in recent days about the demolition work.
"I knew that was going to collapse sometime soon, and it did today," roofer Patrick Glynn told CNN affiliate WPVI.
"For weeks, they've been standing on the edge, knocking bricks off, pieces off. You could just see it was ready to go at any time. I knew it was going to happen. I seen it. I said it 10 times. Ask these guys. Every day, I said, 'It's gonna collapse. It's gonna collapse.' "
Minerva Pinto works nearby. She and her co-workers thought the building looked precarious in the days before the collapse.
"We'd all seen in the past week that the building was really unstable because of the demolition," she told CNN's iReport.
But city officials said there were no known violations at the site.
"No violations, no complaints that we're aware of, and all permits were valid," Nutter said earlier.