The staffer is said to have asked a member of National's press team if the petition should be deleted. When they received no response, the staffer deleted it anyway.
When asked about this, and to provide any response on the matter, a spokesperson for Bridges would not comment, saying it was not a National Party matter.
They instead directed comment to Parliamentary Service, which also declined to comment – "Parliamentary Service does not comment on individual employment matters".
Stuff reported the staffer in question was out of the office, on leave.
The petition disappeared from the National Party website not long after the attack in Christchurch.
A spokesperson subsequently told media that it had been "archived some weeks ago" as part of "normal web maintenance".
However, Bridges later told media that, in fact, the petition had been deleted by an "emotional staffer".
"What had actually happened, I have learned this morning, was that a junior staffer was incredibly emotional on Friday night and took it upon themselves to delete it – we didn't know that until this morning."
He said he is not involved in website maintenance – "it's not something I give a moment's thought in my role as leader of the National Party".