What we've learned 3 weeks after the Parkland shooting -- and what's next

It's been three weeks since they lost 17 classmates and teachers in a tragedy that's still unraveling. In that time, grieving students launched a nationwide movement that could spur new gun laws faster than any previous massacre did; warning signs that were ignored before the shooting came to light; and gun control legislation is gaining traction in the state legislature.

While Florida lawmakers debate that bill, a grand jury could decide Wednesday whether ex-student Nikolas Cruz should be charged for the 17 deaths.

Here's what we've learned in the aftermath of the shooting, and what's happening next:

The students

What's new: Wednesday marks the first full day of classes at Stoneman Douglas High School in Parkland, Florida. Many of the students have confronted state and congressional lawmakers, demanding a ban on assault weapons similar to the one used to kill 17 students and teachers.

What's next: Stoneman Douglas students say they will continue the fight to ban assault rifles. "I'll definitely be speaking out still until changes are made,' Senior Demitri Hoth said.

On March 14, exactly one month after the gunman killed 17 people at the school, students across the country will walk out for 17 minutes in support of the Stoneman Douglas students.

And on March 24, gun control activists nationwide will participate in the March for Our Lives in Washington. The event was created by Stoneman Douglas students.

The legislation

What's new: Florida House representatives are debating a bill that would raise the age for buying firearms to 21; require a 3-day waiting period for purchases; and allow some school staff members to be armed on a volunteer basis.

Senate Bill 7026 -- dubbed the "Marjory Stoneman Douglas High School Public Safety Act" -- would also give law enforcement more power to seize weapons and ammunition from those deemed mentally unfit and provide additional funding for mental health services and armed school resource officers.

What's next: Time is running out for the House to vote on the bill, since Florida's legislative session ends this week. And there could be more complications: Republican Gov. Rick Scott has said he's concerned about the ideas of a 3-day waiting period and arming teachers in school.

The investigation

What's new: The case now involves a complex web of finger-pointing as to who could have helped prevent the massacre, and what signs about suspect Nikolas Cruz were ignored or missed.

Much of the recent blame has fallen on the Broward County Sheriff's Office. One of its armed deputies stayed outside the school as the massacre unfolded. And in the past decade, authorities received more than 20 calls about Cruz and his family.

The sheriff's office recently launched a website "setting the record straight." It says while deputies did respond to Cruz's home multiple times in the past, there was nothing criminal nor dangerous happening that would warrant an arrest.

What's next: Many more details may come to light after a grand jury determines whether there is enough evidence to indict Cruz on 17 counts of premeditated murder. The grand jury could make a decision as early as Wednesday.

And on Wednesday night, Parkland residents will have a chance to grill local officials and authorities at a city commission meeting.

The suspect

What's new: We now know that last year, someone using the name "nikolas cruz" posted a chilling comment on YouTube: "im going to be a professional school shooter." The FBI was warned, but didn't notify local law enforcement.

Others who knew Cruz growing up described him as deeply disturbed, saying he tormented animals, threw rocks at cars, and sometimes introduced himself by saying, "I'm a school shooter."

What's next: Cruz is expected to be formally charged with 17 counts of premeditated murder after a grand jury meets Wednesday.

In the meantime, he will sit in the Broward County Jail, where he was segregated from the other inmates for at least the first week.