John Gill Commentary 2 Chronicles 24:21

"And they conspired against him, and stoned him with stones at the commandment of the king in the court of the house of Jehovah." — 2 Chronicles 24:21 (ASV)

And they conspired against him
Consulted together to take away his life, and got the order of the king to do it:

and stoned him with stones at the commandment of the king in the court
of the house of the Lord ;
where he had stood and reproved them; this they did before he went out, while in the temple; and if he is the same Zechariah, as some think, our Lord speaks of, he was slain between the temple porch and the altar, (Matthew 23:35) , (See Gill on Matthew 23:35).