Nicolas Cruz, the 19-year-old believed to have killed 17 people when he opened fire at Stoneman Douglas High School in Parkland, Florida, was expelled from the school about a year earlier for disciplinary issues, police said.

WSB-TV reported that Broward County Sheriff Scott Israel said Cruz, 19, was expelled for disciplinary issues but did not elaborate.

A student told local reporters that the teen was “troubled” and claimed he would joke about shooting up the school and knowing the school layout.

READ More: Classmate says Florida school shooting suspect showed off guns, joked about attack on school

“I stayed clear of him most of the time. My time in alternate school, I did not want to be with him at all because I didn’t want to cause any conflict with him, because of the impression he gave off,” the student told WSVN.

Reports indicate that gunshots were heard shortly after someone pulled a fire alarm. U.S. Sen. Bill Nelson told CNN that Cruz was wearing a gas mask and is believed to have used smoke grenades to confuse students who fled from their classrooms.

ABC News reported that the suspect attempted to blend in with the other students as they evacuated.

This is a developing story. Be sure to check back with CrimeOnline for updates as they become available.

[Featured Image: AP Photo/Wilfredo Lee]