What to know this morning: In 5 minutes or less

Everything we're talking about this morning -- what you need to know, in five minutes or less.

1. An Amtrak train that was traveling from Washington D.C. to New York City derailed in Philadelphia last night. At least six people died in the crash, and dozens were injured. The story is developing and an investigation will begin today. Read more here.

2. The U.S. is considering sending military ships and patrols to the South China Sea to challenge Chinese claims to islands it is building there. China reportedly expressed concern, and warned that countries should avoid "risky and provocative approaches to maintain the regional peace and stability." Read more here.

3. Bill Clinton was a guest on "The Late Show with David Letterman" last night, and coyly said that he'd return to the White House ... if Hillary asked him to. (After she wins the nomination and the election, of course.) Read more and see the clip here.

4. Hundreds are still searching for a missing U. S. Marine helicopter following the second earthquake in Nepal. The helicopter lost contact after its crew was heard talking about fuel problems. There are eight people on board -- six Marines and two Nepali troops. Read more here.

5. The U.K. has decided it will publish Prince Charles's secret letters to government officials after a long court battle. The public will be able to read the letters, which are referred to as "black spider" memos because of the Prince's handwriting, on Wednesday. Read more here.

6. A South Korean spy agency said Tuesday that North Korean leader Kim Jong Un publicly executed his defense chief -- reportedly for falling asleep during a meeting and "talking back" to the leader. Read the full story here.

7. A gunman opened fire on a bus in Pakistan that was bound for a Shiite community center, killing 43 people. It's the worst attack Pakistan has seen in months. Read more here.