Anna Kepner’s stepbrother allegedly choked her “for minutes” as his final “barbaric” act in her murder … according to prosecutors.

In a newly unsealed transcript from a February hearing obtained by TMZ, prosecutors described how they say Timothy Hudson -- Anna’s 16-year-old stepbrother -- killed her … claiming he put her in a chokehold until she suffocated to death.

Prosecutor Alejandra Lopez described it as “a barbaric, intentional, thoughtful act,” saying "[w]hile she struggled to breathe for minutes, he continued to hold her neck in that manner so that she would die from lack of oxygen.”

She added that Hudson "could have let that hold go" at any time and "allowed the victim to breathe," adding that "instead, for minutes, he held that position in order for her to die and kept squeezing.”

Hudson has been charged with raping and murdering his 18-year-old stepsister on a Carnival cruise ship.

Prosecutors were trying to convince the judge to keep Hudson in custody ahead of his trial, but the judge ruled Wednesday that Hudson could remain free on bond. He’s currently under the care of his uncle.