John Andrew Howland's 14-year-old son, Jayden Andrews-Howland, was last seen boarding the No 3 bus into the Christchurch CBD shortly before the magnitude 6.3 quake hit on February 22, 2011, having been let out of school early because of a teacher-only afternoon.
The bus was crushed by falling masonry on Colombo St.
Howland (41) moved to Greymouth after the tragedy.
Today, he appeared at the Christchurch District Court on a charge of assault after Mr Brownlee had an ice cream container filled with what the minister described as "pretty mucky stuff" tipped over his head at the service yesterday.
Through a duty lawyer, Howland pleaded guilty. The lawyer said his client accepted the police summary of facts.
The case had to be considered for a restorative justice conference, but the duty lawyer said Howland was "not keen to do that".
Outside court, Howland said the Government was "just heartless ... no compassion".
"They're not taking care of all the [quake] families - like us, and everybody else," he said.
"There needs to be more support, more communication, and just compassion really."
He criticised Mr Brownlee for not acknowledging the families at the memorial service.
"He could've come over and said something but he didn't, he walked right past."
Howland prepared the mixture of flour, egg, vinegar, salt, pepper and cocoa at home before driving to Christchurch on Saturday.
He thought about throwing it over Prime Minister John Key instead of Mr Brownlee.
"If Brownlee wasn't there, I would've got Key," he said.
He hopes he made his point. It would've been his son's 20th birthday today.
"It's hard. It doesn't get any easier. Especially around birthdays and anniversaries," he said.
When Howland's case was recalled later this morning, the duty lawyer said his client now wanted to participate in a restorative justice conference with Mr Brownlee.
Judge Jane Farish remanded him on continued bail for the meeting to take place ahead of sentencing on March 15.
Bail conditions included a non-association order with Brownlee - which will be relaxed to allow the restorative justice meeting - and for Howland to reside at his Greymouth home.
As the matter was now sub judice, Judge Farish advised Howland and the media not to conduct interviews before sentencing.
Howland's attack was pre-planned, with the brown sludge being prepared earlier in the week, police said.
Howland later told them that he "didn't like" Mr Brownlee or the National Party.
