KNOW IT ALL: Friday's Top Stories at NBC News

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Good morning — and TGIF! Here are some of the stories we're following today:

College tour bus in fiery fatal crash on Calif. freeway

Ten people were killed Thursday afternoon after a tractor-trailer collided with a bus filled with high school students bound for a college tour. At least five of the fatalities were students. Read more in at NBCLA.

Pistorius trial: Olympian tried to apologize to girlfriend’s family

The third day of grueling cross-examination of Oscar Pistorius included a bright spot for the accused killer: The mother of his victim backed up the athlete’s claims that he tried to apologize in private, countering claims by the prosecution the public apology he gave was grandstanding. Read more in NEWS.

Black box rumors unfounded in missing jet hunt

Are they zeroing in or not? Australia’s prime minister says the search area has been narrowed and searchers are “very confident” the signals they are detecting are from the black boxes of the missing Malaysia Airlines plane, but the man leading the search effort said Friday a new possible signal detection is likely not related to MH370. Read more in NEWS.

108 hours: Inside the hunt for the Boston Marathon bombers

Through interviews with survivors, law enforcement officers and witnesses, NBC News has retraced the frantic hunt for the perpetrators of the Boston Marathon bombing. Read more in INVESTIGATIONS.

You're out! Sebelius' rocky Health Department reign over

Katthleen Sebelius, who oversaw the bug-ridden rollout of a federal health insurance program that she herself called "miserably frustrating," is resigning as secretary of Health and Human Service. President Barack Obama on Friday will nominate Sylvia Mathews Burwell, currently director of the White House Office and Management and Budget, to succeed Sebelius. Read more in NEWS.

NBC News' Chuck Todd predict's Burwell's confirmation won't be easy sailing:

Woman slings shoe at Hillary Clinton during speech

A woman was taken into custody after hurling what she said was a shoe at Hillary Clinton during a Las Vegas speech — and the former secretary of state was quick with a witty comeback. The bizarre incident happened just moments after Clinton took the stage Thursday at an Institute of Scrap Recycling Industries meeting at the Mandalay Bay Hotel & Casino. Read more in NEWS.