NYPD Chief of Department John Chell has been on the force for over 30 years, but the "mayhem" from Monday's Midtown Manhattan shooting now ranks among the worst he's ever seen."I was down there in 20 minutes as the incident commander, and… We [had] casualties in the lobby, one of our own – Officer Islam," he said Wednesday on "Fox & Friends." "We got a mom executive dead. We have a security guard who fought but lost his life. We have an NFL employee who was shot but tried to call his friends up in the NFL. We had [the perpetrator's] car in front… we thought there might be explosives in there. A 44-story building, people running out. This is not normal, and I got cops trying to negotiate, calls coming in to people trapped, a shooter up on the 33rd floor. It was just mayhem." NYC SHOOTING TIMELINE SHOWS GUNMAN MOVED WITH SPEED IN CROSS-COUNTRY DRIVE THAT ENDED WITH OFFICE BLOODSHEDNYPD officials were put on high alert this week when Nevada-based gunman Shane Tamura entered a Manhattan skyscraper and gunned down four people, including NYPD officer and father of two, Didarul Islam.NYC Police Commissioner Jessica Tisch said a suicide note found in Tamura's possession speaks to a possible motive, noting he blamed the NFL for his potential diagnosis and mentioned a 2013 Frontline documentary on Chronic Traumatic Encephalopathy (CTE).MANHATTAN HIGH-RISE SHOOTING VICTIMS: NYPD OFFICER, BLACKSTONE EXECUTIVE AND SECURITY GUARD AMONG THOSE KILLEDThough Chell went on to describe the crime scene as "horrible," he indicated the timing could have been worse."Thank God this didn't happen a half hour earlier," he said."There were minimal people up in Rudin Management… They had safe rooms, they practiced [for these situations]. "The first floor, the security guard who lost his life, he had the recall button for the elevators. These things happen so fast… but when [the gunman] gets to the top floor, he sees a maid who's been there for years…"She's just cleaning up, doing her job, and then… he's firing AR-15 rounds at her, and thank God she got away… and then we had the employee that was at a cubicle that lost her life – a young, rising star in that department. The crime scene, the video, in three decades of doing this, it was just horrible."