Squeezed between two infant seats in the back of Seth Mnookin’s Subaru Forester, I found it almost impossible to know what was going on. The engine was probably roaring, I knew, but I couldn’t hear it over the sirens of the passing police cruisers — a steady stream racing past us and into Watertown. Seth’s iPhone was producing noises I’d never heard before. Gunfire sounds more like punctuated static than a “pop” over police scanners. My iPhone advised us to turn — the path illuminated on the screen was a dull glow compared to the string of flashing lights pointing us to the scene.

I’d hooked up with Mnookin and photographer Brian D’Amico at MIT. When I got a text message from my girlfriend, “There is a shooting at MIT,” I tied my shoes, took my laptop, and headed out the door. I ran across the Massachusetts Avenue bridge. “On my way to MIT,” I tweeted. “Will update ASAP.” Officers sent me to Main Street, where cameras were already set up and a string of police line made its way across the road. “Large media presence already,” I tweeted, showing a picture of the TV trucks on the scene. Mnookin sent me a Direct Message right away. He was there too. He came over and introduced himself, and, being an MIT professor, explained the layout of the area. We stood idly as police pushed us further back. I tweeted updates about the number of police cars and where they were from, and where Main St. was closed. There was no hope of discovering the victim’s identity, and the police didn’t want to talk. Via Twitter, we learned that the officer who’d been shot, died. Police began to pour out of the crime scene. Not “situation-resolved-let’s-get-back-to-the-station” pouring, but “engine-rumbling-that-reporter-better-move” pouring. They were going somewhere.

Having been relegated to foot travel for my three years in Boston, I shrugged. End of the line for me.

‘“I brought my car,” Seth said. I knew who he was, but we’d only just met. I couldn’t tell if he was a maniacal professor or a reporter with a nose for the news. He teaches at MIT, so the odds were split. Amico and I hopped in and Seth unplugged his headphones and the chatter of a very excited police department filled the car. I couldn’t make out what they were saying, but Seth hit the gas. “Where’s 800 Memorial?” The shooters had jacked a car and kicked their victim out at a Shell station. When we pulled up, there were about five police cars and the Shell station was taped off. Nothing was going on. We walked around, took some photos, and checked Twitter.

“Lowjacked to Watertown,” I read aloud. I hadn’t looked up and Seth was making for the car. “Let’s go,” he said.

Again I climbed between the child seats in Seth’s car, a routine that was becoming almost comical. I wedged myself in there and asked for an address.

As we drove, the mood in the car shifted from boyish thrill — what reporter doesn’t dream of being in front of the pack, chasing a story before the police arrive? — to serious. Officers were yelling to each other amid gunshots. “They’re throwing explosives!” we heard. Seth didn’t react, eyes focused on the road. He’d been to Iraq, he’d covered the D.C. Sniper. If I was going to be safe on this scene, it would be with him.

We pulled up behind the last cruiser, which had just stopped in residential Watertown. I climbed over the seat and stayed close to the edge of the road. An officer was jogging down the road past us and called out a warning.

“We got shots fired. Somebody's throwing explosives,” he said to us. I tweeted the quote and stopped walking. It was a dark, unfamiliar street full of flashing lights and scared people with guns. But then they were running back to their cars, taking off down yet another street. We debated taking the car. Brian wanted an escape plan if things went bad. Seth wasn’t so sure. We drove as far as we thought we could and parked. I got out of the car slowly, leaving my bag behind. If there was going to be a gunfight, I wouldn’t be wearing a messenger bag. I looked for a street sign. Nichols and Dexter, it said. An officer hurried past, gun drawn. This was real now.

“Identify yourselves!” a voice boomed. I turned quickly into the bright light pointed at my face. I might’ve hesitated long enough to enjoy a faceful of pavement, but Seth snapped off, “Press,” all of our hands instinctively raised. The man with the light paused. “Screw!” a voice from behind us. Seth: “Where?” I was still trying to figure out how to identify myself, knees shaking, as Seth carried the circular conversation quite well. “Screw!” again.

“Where do we go?”

“Get out of here!”

In an unintentionally confrontational voice, I somehow got a “tell us where to go” out of my throat.

“Can I at least move my car?” It was no use.

“Screw!”

We chose a street and jogged a block. They were arresting a driver. America would see him later, naked, loaded into a police car.

The police line went up. Seth tweeted every aspect of the arrest. I was in a daze. By now, Seth had figured out that he, Brian, and I might very well be the only three reporters watching the arrest of the Marathon bomber. I was still thinking a simple 7-Eleven robbery had gone out of control. A comically off base assumption, considering the police response and explosives, but it was late. I hadn’t slept much since covering the bombing Monday. I was again live-tweeting what I thought was an amazing metro story, and it again became the center of national attention.

People had caught on, and I couldn’t even get all my incoming @ replies to load in one refresh. Seth had more. We fell into a rhythm. Things were happening fast, and it was impossible to know which shouted command from police would be the most important quote of the whole night.

“Are you tweeting that?” I’d ask.

“Yeah.”

“Okay, I’ll retweet. Brian, do you see anything?”

We almost always had at least one pair of eyes on the action, and we almost always had tweets going out when something was happening. When it seemed like there was no update to give, we just weren’t looking hard enough. I glanced down cross streets, watched the photographers with the big lenses. Seth, I’m sure, had his own cues. Brian, an experienced breaking news photographer, knew what to look for when police moved around a crime scene. We’d talk a lot sometimes. Should we move? Did you hear that? What’d they say? Scanner says the suspect was hit. Did you see an ambulance?

The crime scene started to fade. Cars were leaving one by one. A State Police spokesman, David Procopio, updated us. Seth and I tweeted quotes furiously.

“One more suspect at large.”

“One accounted for,” I tweeted. Press would be staged at another area. This scene was mostly done, Procopio said. We could stay, but there would be no more press briefings.

Seth’s car was well inside the police perimeter, and we weren’t getting to it any time soon. Our laptops and charging cables would have to wait for us.

A gracious L.A. Times reporter, whose name I forget, gave us a ride to the staging area and allowed me to charge my phone.

In the car, I got a tweet from Wired’s Adam Rogers in response to the news that I was heading to the staging area.

“And that's the end of on-scene usefulness. Sorry, Taylor.”

It was true. Anything I would find out at the media staging area would be streaming live to TV audiences everywhere. We were done. We kept tweeting updates and answering questions. People nearby offered to bring us phone chargers via Twitter. Someone offered me a sandwich. Around 4:30 a.m., we cleared out. The news had broken, and we’d been there.

I collapsed into my office chair at 5 a.m. Boston was being closed down, one system at a time. We were entering lockdown, and we’d left just in time. I replied to tweets and followed others I knew were still on the ground.

At around 7 a.m., my groggy roommate walked into my room, rubbing his eyes.

“Dude,” he said, reading alerts on his phone, “did you hear what happened?”