Sergeant John Coughlin was killed in the  September 11, 2001, terrorist attacks while attempting to rescue the victims trapped in the World Trade Center.

He was assigned to ESU Truck 4.

Sergeant Coughlin had been employed with the New York City Police Department for 18 years, and is survived by his wife, three daughters, mother, and brother. He was also a member of the Thiells Fire Department in his hometown of Pomona, NY

He was posthumously awarded the New York City Police Department's Medal of Honor for his heroic actions.

72 officers from a total of eight local, state, and federal agencies were killed when terrorist hijackers working for the al Qaeda terrorist network, headed by Osama bin Laden, crashed two of four hijacked planes into the World Trade Center towers in New York City on the morning of September 11, 2001. After the impact of the first plane, putting the safety of others before their own, law enforcement officers along with fire and EMS personnel, rushed to the burning Twin Towers of the World Trade Center to aid the victims and lead them to safety. Due to their quick actions, it is estimated that over 25,000 people were saved.

As the evacuation continued, the first tower unexpectedly collapsed due as a result of the intense fire caused by the impact. The second tower collapsed a short time later. 71 law enforcement officers, 343 members of the New York City Fire Department and over 2,800 civilians were killed at the World Trade Center site.

A third hijacked plane crashed into a field in rural Pennsylvania when the passengers attempted to re-take control of the plane. One law enforcement officer, who was a passenger on the plane, was killed in that crash.

The fourth hijacked plane was crashed into the Pentagon in Arlington, Virginia, killing almost 200 military and civilian personnel. No law enforcement officers were killed at the Pentagon.

The terrorist attacks resulted in the declaration of war against the Taliban regime, the illegal rulers of Afghanistan, and the al Qaeda terrorist network which also was based in Afghanistan.

On September 9, 2005, all of the public safety officers killed on September 11, 2001, were posthumously awarded the 9/11 Heroes Medal of Valor by President George W. Bush.

The contamination at the World Trade Center caused many rescue personnel to become extremely ill. The first death of a law enforcement officer linked directly to the aftermath of 9/11 occurred on January 6, 2006, when Detective James Zadroga, of the New York City Police Department, died from inhaling the noxious gases present at the site.