Story highlights Prosecutor: "This arrest is not the end of the grand jury's investigation"

Griffin Campbell is charged with six counts of third-degree murder

The contractor also faces involuntary manslaughter and reckless endangerment charges

The building's wall collapsed on a Salvation Army store in June, killing six people

A contractor connected with a fatal building collapse in Philadelphia now faces murder charges.

Authorities say Griffin Campbell, 49, was overseeing a building demolition in June when a four-story wall collapsed onto an adjacent Salvation Army thrift store , killing six people and injuring 13.

Now Campbell is charged with six counts of third-degree murder and six counts of involuntary manslaughter, the Philadelphia District Attorney announced on Monday.

Campbell also faces charges of recklessly endangering another person, causing catastrophe, risking catastrophe and criminal conspiracy.

Attorney William Hobson, who is representing Campbell, told CNN his client would plead not guilty to the charges.

According to a statement released by District Attorney Seth Williams, Campbell decided on the method of demolition.

A day before the collapse, Campbell removed bricks and braces that had supported the wall, even though an architect warned him not to, the statement said.

Campbell promised to build scaffolding to support the wall and said he would reduce its height to the roofline of the Salvation Army building, the District Attorney's Office said.

"In reality, however," the statement said, "Campbell was unwilling to pay for enough labor to perform the task."

Campbell surrendered himself to police Monday afternoon, his attorney said. Hobson said he expects bail to be set at $1 million, with plans to seek a reduction.

"I hope Griffin Campbell's arrest today will give the victims and their families some small sense of relief, though I know their pain will never go away," Williams said on Monday.

The prosecutor also announced Monday that crane operator Kary R. Roberts -- also known as Sean Benschop -- is facing an additional charge of criminal conspiracy in the case.

Roberts is currently in jail awaiting a preliminary hearing for involuntary manslaughter and other counts, after police said toxicology results showed he was under the influence of a controlled substance at the site of the collapse.

He has maintained his innocence. In June, his attorney, Daine Grey Jr., said his client was "being made the scapegoat in this situation."

Williams said it is unclear at this point whether a grand jury will find more evidence of wrongdoing by others.

"This arrest is not the end of the grand jury's investigation," the statement said.