In a final message before taking his life, the lead building inspector responsible for a Center City building that collapsed last week said he was to blame for the deadly disaster.

"It was my fault. I should have looked at those guys working, and I didn't," Ronald Wagenhoffer said in a video recorded on his cell phone.

NBC10 Philadelphia has learned the 52-year-old veteran Philadelphia Licenses & Inspections staffer recorded the one-minute long message for his family.

Wagenhoffer was found dead around 9:30 Wednesday night of an apparent suicide, city officials confirmed at a press conference Thursday.

Law enforcement sources say Wagenhoffer shot himself once in the chest inside his pickup truck along a wooded section of the 100 block of Shawmont Avenue in the Roxborough neighborhood of Philadelphia. That's less than a mile from his home.

In the video, Wagenhoffer says he couldn't sleep and blamed himself for the building collapse at 2136 Market Streets that killed six and injured 13 when the building collapsed onto a store on June 5.

He admitted he never truly inspected an adjacent work site after a citizen complained about safety concerns, although he reported there were no violations found.

"When I saw it was too late. I should have parked my truck and went over there but I didn't. I'm sorry," Wagenhoffer said in the message.

City officials said Wagenhoffer was sent to the demolition site of 2134 Market Street on May 14 -- that's adjacent to the building that collapsed at 2136 Market Street.

The inspection was set to take place after Center City resident Stephen Field complained to the city's 311 call center about a lack of safety equipment on workers and adequate protection of the sidewalk. The city has been saying for a week that no issues were found.

Last Wednesday, the four-story outer wall of 2136 Market Street crumbled onto the Salvation Army Thrift Store next door. Six people were killed in the collapse -- three employees and three patrons. The wall also buried 13 others who were in different areas throughout the store, including the basement. They were eventually rescued by citizens and first responders.

Excavator operator Kane R. Robert, also known as Sean Benschop, stands charged in the collapse. Investigators with the District Attorney's homicide unit say he tested positive for the pain killer Percocet and marijuana on the day of the collapse. They allege he was in no condition to operate heavy machinery. A grand jury has been convened to investigate the circumstances surrounding the collapse.

L&I records also show Wagenhoffer completed and passed an initial inspection at 2136 Market Street on Feb. 25.

City officials said that fellow employees and L&I Commissioner Carlton Williams reached out to Wagenhoffer in the days after the collapse.

"This man did nothing wrong," Deputy Mayor Everett Gillison said at a press conference Thursday. "The department did what it was supposed to do under the code that existed at the time."

In a tweet posted Friday afternoon, Mayor Nutter's Press Secretary Mark McDonald refuted NBC10's reporting of the video message.

"NBC10 falsely stated that L&I inspector said of collapse -- "It was my fault." That is a total lie," he wrote.

NBC10 Vice President of News Anzio Williams said, "We have seen the video. We are standing behind our journalism." In a phone conversation with Williams, McDonald maintained his belief that the report was inaccurate.

A source close to the investigation who did not want to be named because they aren't authorized to speak publicly about the case, said Wagenhoffer had been grieving for days. They said Wagenhoffer did not take any time off after the collapse because he thought sticking to his work routine might help him deal with the tragedy.

On Thursday, Nutter, who is in Chicago, was asked if Wagenhoffer should have been placed on leave after the building collapse.

"Each of us deals with our grief and sorrow and any sense of responsibility in a different way. I'm not going to second guess his judgment to keep working," Nutter responded. He said Wagenhoffer had been in constant contact with his supervisor and was offered time off, but declined.

"I think what you have here is a 16-year-employee who cared very deeply about his job," said Nutter. "We don't know all the things that may have been going through his mind."

Commissioner Williams called Wagenhoffer an outstanding employee.

“He was a dedicated civil servant who did his job," he said. "He started in the Department of Public Property and moved his way up through the ranks as one of our top code officials in the Department of Licenses & Inspections."

Nutter said the city is also encouraging other employees to get emotional support if they need it.

"Obviously I don't know why this happened, but we've tried to send a message out certainly to all of our public employees who are deeply affected by this, especially those who worked with Ron," Nutter said.

Wagenhoffer leaves behind a wife, Michele and a son.

Deputy Mayor Gillison added there are five investigations underway regarding the collapse and that the city is "proud" of L&I's work.

Griffin Campbell was the contractor overseeing the demolition. In a statement released by his attorney Kenneth Edelin, he said "heartfelt condolences go to the family of the inspector."

"We also continue to pray for the families of those that were lost, and for the health and speedy recovery of those that were injured," the statement continued.