It's not true until it's been proven and so far there's no evidence to prove that Crime Junkie and it's hosts Brit Prawat and Ashley Flowers plagiarized any of their content.
Starting around August 12th, 2019, rumors swirled on Reddit, Twitter and Facebook that the podcast was copying research from other podcasters and journalists. The problems with these rumors is that so far, none of them are substantiated by hard proof that plagiarism indeed occurred by failure to cite sources. In fact, on Crime Junkie's official site you can find a full episode list with the sources for each individual episode listed and linked.
If you want to dig into legalities here, Crime Junkie, Flowers and Prawat have almost certainly lawyered up and if individuals continue to post claims of plagiarism against the duo without valid sources, they may find themselves up against the podcast in some hefty defamation suits in the near future.
This whole mess can serve as a reminder to content creators from every corner - cite your sources and cite them often, both verbally and in writing! It can also serve as a reminder to anyone tempted to post rumors to social media, that anything you post can be screenshotted and used against you legally. If you make false claims (or claims without evidence) you may find yourself in a legal pickle.