Darius Parker is a relative of Odafin Tutuola through his ex-wife Teresa Randall.
Background
Darius was the product of the incestuous rape of Teresa Randall (who is Detective Tutuola's ex-wife) committed by his grandfather. Teresa told her mother the truth but was not believed while being forced to give birth to Darius. Darius is the half-brother of Ken Randall (who is the son of Fin and Fin's ex-wife and who unlike Darius was raised by his mother). Darius was raised as Ken's cousin but learned the truth from his grandmother's dying words. He wished his grandmother had never told him that and that she had instead taken that knowledge to her grave. He eventually grew to hate his mother for not raising him and for threatening him when he was twelve. He also hated Fin and himself. Nevertheless, he had a close bond with Ken after their relationship came to light.
In 2003, when his then-girlfriend told him his knife was accidentally left at Nina Stansfield's apartment, he left to get it. While there, he rapes Nina with the knife and then stabbed her to death because he believed she was a bad mother. He then killed her infant son Stevie by burying him alive with the help of his then girlfriend, to free him of having to live a bad life. He eventually committed various other crimes like burglary, assault, and trafficking narcotics.
On SVU
He later confesses to Ken, who protects Darius by refusing to reveal his confession and later claiming the crime has a different culprit, inventing a bogus story to support this claim. Darius confesses to committing the crime and helps the police find the bodies. Darius knew that since he did not have a lawyer with him that all evidence found would be inadmissible in court. When the police find extra evidence, Darius does not accept any deals, despite his lawyer's advice. He says that he wants his day in court and threatens to blackmail the SVU detectives. (SVU: "Venom")
Darius makes good on these threats and with the help of a corrupt cop he exposes the bad things that the detectives did, such as Elliot Stabler sweeping his daughter's DUI under the rug and Olivia Benson helping her fugitive half-brother. Darius later confronts his mother on the stand, condemning her for all the years of harsh treatment though he is shocked to learn of his paternity but denied this. However, it was shown that a part of him did believe this knowledge but could not get over his anger towards Teresa for her treatment of him. He is soon found not guilty at trial. Shortly after the trial, he meets Ken and Fin who both promptly disown him for what he did to his victims and the good detectives. After a warning from Fin, Darius believed that Fin will always be looking over his shoulder for him, but Fin announces he won't bother with him, promising to never think about Darius again but knows Darius will always be in fear of that. Indeed, Darius was unnerved by this statement and could only watch as Fin and Ken walk off. (SVU: "Screwed")