By Faith Karimi and Holly Yan, CNN

(CNN) -- A month ago, a former student roamed the halls of Marjory Stoneman Douglas High, opening fire on terrified students and teachers at the Florida school.

The massacre of 17 students and faculty members added to a grim statistic: three of the 10 deadliest mass shootings in modern US history happened within five months of one another.

In the four weeks since the Valentine's Day shooting, the survivors have turned into activists on the national stage. Even as they grieve, they've demanded action on gun reform. In between congressional meetings and protests, they've attended memorials and funerals.

Here's what we've learned since the shooting:

The students

Many of the students have confronted state and federal lawmakers, demanding a ban on weapons similar to the gun used to kill their friends and teachers.

Students across the country plan to continue the fight for gun reform Wednesday by walking out of class for 17 minutes -- one for each person killed in Parkland -- starting at 10 a.m. local time.

Some schools are allowing students to walk out and are providing additional security to ensure safety while others have forbidden participation.

From there, the students will turn their attention to March 24, when gun control activists nationwide will participate in the March for Our Lives in Washington. The event was created by Stoneman Douglas students.

A local March for Our Lives is also planned for that day in Parkland, for people who may not be able to make it to the nation's capital.

The investigation

Nikolas Cruz confessed to the shooting, and will be arraigned Wednesday on 17 counts of murder and 17 counts of attempted murder. He plans to stand mute, which means a judge will enter the plea on his behalf.

Cruz remains in the Broward County Jail, where he's segregated from other inmates. Prosecutors announced in court filings Tuesday that they will seek the death penalty. They listed several factors, including that Cruz knowingly created a risk of death for many people and that the shooting was "especially heinous, atrocious or cruel."

His attorneys had previously indicated he is willing to plead guilty to avoid the death penalty. Prosecutors asked the court to put several provisions in place in the event his defense should introduce his mental health. Cruz's defense team has said he battled with mental illness and depression after his adoptive mother died.

The case will involve a complex web of finger-pointing on who could have helped prevent the massacre, and what signs authorities missed about the confessed gunman.

The legislation

While not much has changed on the federal front, there have been some changes on the state level.

Florida Gov. Rick Scott signed Senate Bill 7026 into law last week, the first gun control legislation in the state after the massacre.

The law, known as the Marjory Stoneman Douglas High School Public Safety Act, tightens gun control in several ways, and also allows some teachers to be armed.

The National Rifle Association did not especially like a provision of the law that raises the minimum age to purchase a firearm from 18 to 21. It immediately filed a federal lawsuit against Florida, saying the age mandate violates the Second and 14th Amendments to the Constitution.

A controversial part of the new Florida law allows for the arming of some teachers if the local school district and local sheriff's department agree. A few days after that bill passed, the White House proposed providing some school personnel with "rigorous" firearms training, and backed a bill to improve criminal background checks on gun buyers. It backpedaled on the idea of increasing the minimum age to buy certain firearms -- a policy President Donald Trump had said he would support.

The school district

The Broward County school board passed a 24-point resolution last week calling for Congress to ban assault weapons, require universal background checks and broaden the perimeters of school gun-free zones. But unlike state and federal officials, the school board slammed the idea of arming teachers.

Superintendent Robert Runcie said he wants an immediate, independent review of the social and educational history of Cruz. It will include a review of his academic records, interviews with staff members who worked with him, and an analysis of any social and emotional help he may have received. Runcie estimated the investigation would take 10 weeks and cost $60,000.

Meanwhile, a student who was shot five times plans to sue the school district, the county, and the local Sheriff's Office.

The local authorities

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.

Embattled Broward County Sheriff Scott Israel has rejected calls for his resignation amid accusations that his department's incompetence failed to stop the gunman.

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