Brereton, who acknowledged his friendship with sacked Saints coach Scott Watters, described Pelchen as a football myth who would never gain a job at another club.
Describing the sacking as pathetic, Brereton said he was shattered for Watters.
Brereton added all other 17 clubs would now win ahead of the Saints.
"This is a pathetic decision driven by a certain sector in the football department that is cancerous," Brereton told SEN.
Brereton said Watters was among the three smartest football people he had met but paid the price for opposing Pelchen.
"The three strong football people who opposed him (Watters, football manager Greg Hutchison and senior assistant coach Dean Laidley) are no longer there," Brereton said.
Brereton also said he doubted Watters knew he was about to be sacked when he also gave an interview on Friday morning with SEN.
At the same time, the Saints board was holding a meeting where Watters' fate was sealed.
"This has been hatched away from the sunlight," Brereton said.
"We always over-dramatise certain things, but there's someone with a lot of blood on their hands tonight."
Brereton was then asked to whom he was referring and he made it clear it was Pelchen.
"There are a lot of myths in footy and we're talking about one of them," he said.
Pelchen also used to work at Hawthorn, where Brereton made his name as a player and was a club director.
"Chris wants to make sure of his job at St Kilda because I guarantee you, the word has gone around," Brereton said.
"He won't get another one elsewhere."
Brereton said fellow AFL strugglers Melbourne were now miles ahead of St Kilda.
"Thank God for St Kilda, because 17 other clubs are going to win before them," he said.
"There's a reason they win one premiership out of every 140 years ... they are the most poorly led from the top club.
"It is the blind leading the blind there."