Dan Kozlowski is the ex-husband of single mother Laura Kozlowski. She had a son named Kendall with her abusive ex-boyfriend James Kendall, who never knew about their son. When James kidnapped Kendall, Laura was harassed by Cindy Marino under allegations of having killed him. This pushed Laura over the edge and resulted in her committing suicide by hanging herself.
Kendall was rescued and treated at the hospital, where James and Dan both appeared for guardianship. A former drug mule, Dan was able to cut a deal in exchange for testifying against the drug dealers that he was working for. After a physical altercation between the two and the squad's attempts to put Kendall in the system, James sues the system for interference. But James lets it slip that he's the kidnapper and ends up arrested, with Dan being awarded custody over Kendall thanks to a posthumous testament from Laura leaving Kendall with Dan. Dan reassured Detective Stabler and ADA Novak that he was clean and sober and that he intended to stay that way in order to take care of his son. (SVU: "Haystack")