Maryellen Seaver is a woman who was kidnapped, raped, and tortured by Brent Allen Banks as a teenager, shortly thereafter escaping by her own efforts. Her personal trauma was what spared her testimony, but Banks was still convicted and imprisoned for several years on presented evidence of the violence Maryellen was put through, such as ligature marks from being bound and numerous bites all over her skin.
When she heard Banks was guilty again of violence, this time of raping, torturing, and murdering a mother and daughter in their apartment, she came to Special Victims and introduced herself, asking what she could do. She sadly couldn't offer her testimony to not bias the jury with Banks' past crimes, which she lamented. Her conversation with Dani Beck led to Andrew Munch, the severely mentally ill uncle of John Munch who was eavesdropping, to kill Banks in an act of vigilantism. (SVU: "Uncle")