The letter dated Tuesday accuses the department of not upholding Wisconsin's mandatory arrest law in domestic violence cases. It also criticizes them for blaming the victim for not cooperating.
Radcliffe Haughton fatally shot his wife, Zina Haughton, and two co-workers at a Brookfield spa Oct. 21. He wounded four others before killing himself.
Officers went to the Haughtons' home 20 times in the past decade, including at least seven possible domestic violence calls.
The legislators want a transparent investigation of the department's interactions with Haughton and their domestic violence policies.
Chief Steven Rinzel did not respond to a call seeking comment Wednesday.
