It was just after 1 a.m. on Tuesday, and the Dali was loaded down and headed south on the Patapsco River, toward the mouth of the Chesapeake Bay, bound for Sri Lanka, halfway across the globe.

Under a full moon, tugboats escorted the Singapore-flagged container ship out of the Port of Baltimore into the bay. The tugs peeled off at 1:10 a.m. and chugged back to port.

Two miles south, a construction crew of at least eight Latin American immigrant workers were repairing potholes on the Francis Scott Key Bridge, a 1.6-mile-long, 185-foot-high steel structure connecting the southern tip of Baltimore City to Dundalk, in Baltimore County. They worked in the middle of the night, so as not to inconvenience the more than 35,000 motorists who cross the bridge each day.

The moments leading up to and immediately after the Key Bridge’s destruction, one of the largest infrastructure disasters in Maryland’s history, are detailed in video, police and fire dispatch audio, ship location data and in statements from officials.

Late-night drivers and truckers who crossed the Key Bridge at 1:20 a.m. Tuesday might have looked north and seen the Dali approaching, a routine spectacle on the waters outside the port. Millions of tons of cargo — coal, cars, sugar, gypsum and construction equipment — pass under the bridge each year, going to and from a port system that employs more than 15,000.

Drivers along the bridge passed the flashing yellow lights of the construction vehicles parked in the southbound lanes near the bridge’s midpoint. The Dali approached like the countless other boats before it that had passed underneath without issue.

Then, at 1:24 a.m., something went wrong. The Dali’s lights went out, possibly the result of power failure. The giant ship, 984 feet in length, drifted in the dark for a minute before the lights flickered back. Dark smoke poured out of the vessel.

At 1:25 a.m., The Dali veered off course. Ship tracking data shows the boat went to its starboard, or right, side, putting it on a tragic path.

The Dali, at some point, signaled mayday, the maritime code for distress, as the plumes of black smoke, larger now, rose above the deck of the approaching bridge.

Power on the Dali failed again, the ship went dark as it continued to list forward toward the Key Bridge. Its bow lined up with the bridge’s pylon.

A nearby Coast Guard station had received the mayday call; the crew knew impact with the bridge was imminent.

By now, the Maryland Transportation Authority Police were aware of the ship’s condition and quickly moved to stop oncoming traffic. They were calm and decisive, but seemed unaware of the impending peril.

“I need one of you guys on the south side, one of you guys on the north side,” an officer radioed at 1:27 a.m. “Hold all traffic on the Key Bridge. There’s a ship approaching that just lost their steering. So until they get that under control we gotta stop all traffic.”

A second officer headed to the south side of the bridge where he radioed back that he’d stopped traffic for the northbound lanes.

Southbound traffic continued to flow, and the workers remained on the bridge deck. Precious seconds ticked by.

“Is there a crew working on the bridge right now?” one of the officers asked around 1:28 a.m.

“Just make sure no one’s on the bridge right now. … If there’s a crew up there, you might want to notify whoever the foreman is to see if we can get them off the bridge temporarily,” he said.

The last two cars to cross the bridge headed south. Forty-nine seconds later, the Dali crashed into the bridge.

Read more: Full coverage of the Key Bridge collapse

A third officer on the north side of the bridge offered to ride up and tell the workers as soon as another unit came to relieve him.

He did not get the chance.

The Dali, lights off once more, black smoke still spewing, struck the pylon at 1:28 a.m. An engineering professor at the University of Michigan estimated the blow carried the force of 10 million pounds.

Just 20 seconds after the collision, the Key Bridge collapsed into the Patapsco River.

“The whole bridge just fell down,” the second officer said over the radio, his voice in apparent disbelief.

He struggled to find words.

“Start, start whoever, everybody — the whole bridge just collapsed,” he said.

The officer on the north side, the one who offered to ride up and tell the workers, said he couldn’t get to the other side to make sure the lanes on both sides were closed. Luckily, they had been.

Gov. Wes Moore later declared the officers heroes.

“They saved lives,” he said at a mid-morning briefing.

The crew, however, never made it off the bridge, cast into the frigid, dark water below. In the immediate aftermath, two workers were removed from the water, Baltimore Fire Chief James Wallace said Tuesday morning. One was taken to the Maryland Shock Trauma Center, treated and released. The other declined treatment and left the area.

Rescue teams, boats and divers and helicopters, armed with infrared cameras and sonar and underwater vehicles, searched through the night and the day. There was no sign of the six missing workers.

Water in the bay Tuesday morning was around 47 degrees, according to the National Weather Service. At that temperature, the effects of hypothermia can set in within minutes, and a person may lose consciousness after an hour. It is unlikely someone would remain alive much longer.

But officials, in a news conference early that morning, projected hope. Never mind the cold temperatures, changing tides and water so dark and murky divers could barely see in front of them, Wallace said.

Wallace, along with a slew of government officials, addressed the world at 6:30 a.m. On a normal day, the construction crew’s shift would have ended. They might be back home, already in bed.

“We’re going to rely on our experts, our dive teams that are here, to tell us when they’ve reached that nonsurvival point,” Wallace said in the predawn hour.

The sun rose along with the tide. The workers had likely long been dead.

Banner reporters Justin Fenton, Giacomo Bologna, Hallie Miller, Daniel Zawodny, Alissa Zhu, Brenna Smith, Emily Sullivan, Ramsey Archibald, Wes Case and Pamela Wood contributed to this article.