be placed on lockdown
フロリダの学校で銃撃事件が起きました。
Florida high school shooting: Here's what we know
Broward County Public Schools reported the shooting began near dismissal time, when staff and students said they heard the sounds of gunfire.
Some students said a fire alarm sounded before the gunfire. Police say Cruz began the rampage outside before opening fire inside the high school.
Sen. Bill Nelson, D-Fla., told MSNBC that Cruz wore a gas mask and tossed smoke grenades to draw students out into the hallways.
The school was placed on lockdown. Television footage showed students running from the school with their arms in the air, tossing backpacks into a pile. Some students were being treated on the sidewalks and loaded into ambulances.
Cruz was at large before being taken into custody off the school's campus roughly two hours after the shooting.
Police said he was armed with an AR-15-style, semiautomatic rifle and "countless" magazines.
be placed on lockdownを取りあげます。まず、be placedを『ジーニアス英和辞典』（第五版、大修館書店）で調べるとbe well(ideally) placedで「1. （…するのに）良い立場、状況にある 2. （ホテルなどが）外出するのに良い場所にある」とありました。placeの動詞形は「人を良くない立場、状況に置く」としても使われますがputよりも固い言い方のようです。そこに“an emergency measure or condition in which people are temporarily prevented from entering or leaving a restricted area or building (such as a school) during a threat of danger”（Merriam-Websterより）を意味するlockdownがついたbe placed on lockdownは「完全封鎖の状態になる」となります。
容疑者は発砲前に火災報知器を作動させて、外にできるだけ多くの生徒を集めようと企んでいたようです。(flying bird)
