"He was very mistreated. I won't go into details," Jermaine Jackson said in a broadcast interview. "He will come out with the proof very, very soon."
The singer was booked last month after being accused of molesting a boy at his Neverland Ranch outside Santa Barbara, Calif. He has denied the allegations and was released on $3 million bail. Jackson smiled and waved to supporters upon his release.
Jackson still hasn't been charged.
CBS News Early Show National Correspondent Hattie Kauffman reports the family friend says the rough treatment occurred inside the Santa Barbara airplane hangar where Jackson was arrested.
"He has marks on his body to prove that he was physically bruised, and in fact, from what I understand, he has a dislocated shoulder," said Stacy Brown, the friend who appeared with Jermaine Jackson on MSNBC's "The Abrams Report", said.
The Santa Barbara Sheriff's Department denies the charges, saying "Mr. Jackson was treated with courtesy and professionalism throughout the process. At no time was he mishandled or subjected to any form of mistreatment."
"I'm not denying or confirming Jermaine's statement at this time," Michael Jackson spokesman Stuart Backerman told Kauffman
Meanwhile, Jackson's parents are standing behind their son, saying they believe he's innocent.
His mother says some people are just "mean and wicked" in an upcoming television interview.
His parents also say they'll adopt his children if authorities take them away from him.
Mathis Abrams is the child psychiatrist who triggered a Jackson molestation investigation ten years ago. He said recent reports that the alleged victim in this case gave conflicting statements comes as no surprise.
"Children will change their minds. Children may be frightened at first of the system or the whole pressure," he said, adding that children are easily manipulated.
"I think that this is a possibility in both cases, that there could be coaching, but, again, I wasn't given the opportunity in the initial one to even try to find out," he said.
Charges are expected to be filed against Jackson next week.