Detective Howard investigated a murder at the LaCroix mansion.
After they collected a diamond and ruby adorned pendant bequeathed to Bobby Singer by Bunny LaCroix, Sam and Dean were very disappointed with the pawn shop's appraisal of it, but did discover that it was actually a key. When they returned to the LaCroix mansion to investigate further, they were informed by Detective Howard that Bunny's brother Stanton had been murdered and that they, along with everyone else who'd set foot in the mansion that day, were suspects.
Detective Howard set about taking each suspect aside and interviewing them. He was last seen alive standing at the bottom of the spiral staircase, bellowing for Sam to report for his interview, which he managed to avoid. Not long after that, the boys responded to the maid Olivia's screams and found Detective Howard dead, apparently drowned in the toilet.
It was later revealed that vengeful shapeshifter Olivia had murdered Detective Howard as well as Stanton, Phillip, the butler, and Colette, the maid. Dean eventually killed her by shooting her with several silver bullets.