The International Control Systems Incorporated Building (known by its acronym form as ICSI Building) was a corporate building located in downtown Los Angeles that was destroyed by Martin Riggs and inadvertently Roger Murtaugh.
An unknown terrorist, possibly since put into custody by the LAPD, planted a bomb in a car and drove it into the building parking lot. The suspect set the timer and then fled in a timely fashion. However, somebody (a security guard maybe) saw the suspicious vehicle pull into an awkward position and watched as the suspect left. When the witness opened the door (which was left unlocked) he/she saw a timer and feared it was a bomb so authorities were immediately contacted.
Police responded to the scene and made sure all civilians evacuated the building. Just as Team Riggs/Murtaugh arrived in their Chevrolet Caprice squad car, the ICSI building was empty and the police were awaiting the arrival of the bomb squad. When a beat cop told them the building was empty and the bomb squad were on their way, Murtaugh knew then everything would be fine. But Riggs had a plan of his own and wanted to defuse the bomb himself. Despite Murtaugh telling him not to handle it, he gave in and followed him inside the parking lot.
The duo approached the suspect's car, a 1984 Lincoln Continental, and they found the bomb on the passenger's seats. Riggs opens the door on his side of the car (the left) and examines it, commenting on the hardware installed on the bomb. Murtaugh pulls the door on his side a little too quickly, luckily, the bomb did not go off. Both detectives quietly chat about last minute decisions and Murtaugh thinks he and Riggs should have a cappuccino since they're inside the building. But they are not alone; a cat comes by and startles the cops. Then Riggs begins to cut the wires of the bomb. But each time Murtaugh stops him, scared one wrong move will kill them both. Riggs eventually cuts the wire (the red one) and instead of stopping the timer, actually made things worse by speeding up the time of detonation. He tells Murtaugh to grab the cat and they both flee telling everyone to back up as the bomb would now explode any second. It does and the building begins to collapse into dust and rubble. Though there were no casualties in the explosion and no one was injured, but it caused Riggs and Murtaugh to be demoted to uniform duties as patrolmen the following day.