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KNOW IT ALL: Monday's Top 6 Stories at NBC News

From wet holiday travel to threats from North Korea, see the stories we're following.

Good morning, and happy Monday. Here are some of the stories we’re following today:

1. Gunman who ambushed cops: ‘Watch what I’m going to do’

Before Ismaaiyl Brinsley shot two New York Police Department officers, Wenjian Liu and Rafael Ramos, in their squad car, he told two bystanders to follow him on Instagram and said, "Watch what I'm going to do." That Instagram account had anti-government and anti-police posts on it, including the one he had written while traveling to New York: "I'm putting wings on pigs today. They take 1 of ours … let's take 2 of theirs." After Brinsley shot the officers, he fled to a subway station and killed himself. Read more in NEWS.

2. North Korea threatens ‘all the citadels’ in the U.S.

North Korea accused the U.S. government of being involved with the comedy "The Interview" — the film who's release was canceled last week after movie theaters planning to show it were threatened. The U.S. said North Korea is behind the hacking of Sony Pictures, which made the movie, and even though the North Korean government denies that it was involved, it said Sunday its target was "all the citadels." They didn't specify what they meant by citadels, but added: "The army and people of the DPRK are fully ready to stand in confrontation with the U.S. in all war spaces including cyber warfare space to blow up those citadels." Read more in NEWS.

3. Holiday travel: It's beginning to look at lot like .. April?

As Americans take to the roads and the skies to get home for the holidays, a north-south cold front threatens to deliver rain and gusty winds along the Gulf Coast and snow in the Upper Midwest on Tuesday. On Christmas Eve, the storm will move into the Northeast and has the potential to disrupt flights. AAA predicts 98.6 million people will travel at least 50 miles between the dates of Dec. 23 and Jan. 4. Read more in WEATHER.

4. Sydney hostage-taker's partner has bail revoked

An Australian court on Monday ordered the bail revoked for the partner of Man Haron Monis, who last week stormed a Sydney cafe at gunpoint and took 17 people hostage. Three were dead, including the gunman, by the end of the 16-hour ordeal. Monis' partner, Amirah Droudis, was ordered by a Sydney court to return to jail to await trial after being charged in connection with the stabbing murder of Monis' ex-wife. Monis, who had been charged as an accessory to the murder, had been free on bail at the time of the siege. Read more in NEWS.

5. Florida police officer fatally shot and run over

Tarpon Springs Officer Charles "Charlie K" Kondek, a father of five children and a former New York City police officer, was shot Sunday by a man who felt like "a caged rat" and didn't want to go back to prison, investigators said. Kondek was responding to a noise complaint about music blaring from the car of Marco Antonio Parilla Jr. Parilla, out on parole, fired seven shots at the officer and then ran him over with his car as he fled. "He's going back to prison and he can be a caged rat in prison because that's where he belongs," the county sheriff said. Read more in NEWS.

6. Driver shouting 'Allahu Akbar!' runs down pedestrians in France

A driver screaming "Allahu Akbar!" (Arabic for "God is great") appeared to deliberately mow down pedestrians in the French city of Dijon before being arrested on Sunday. The driver veered into pedestrians in five different parts of the city, injuring at least 11 people. A day earlier, French police shot and killed a man also shouting "Allahu Akbar," who had stabbed and wounded three officers in a police station. Read more in NEWS.

And now this ...

When most people think of drones, they think of the sky. But the Navy has developed a drone for the sea, and it looks like a shark. Cue the "Jaws" music.