University of Iowa police arrested 12 students in the latest step of an investigation spanning several weeks, authorities said.

Police charged nine students at Currier and three at Mayflower in related busts Monday night.

Must charges were drug related — 10 for marijuana and three for prescription drugs — but they also included criminal mischief and possession of burglar’s tools. The charges range from serious misdemeanors to Class D felonies, which are punishable by up to five years in prison.

A bust of this magnitude —18 officers were involved — is unusual for the UI dorms, said Assistant Vice President for UI police Chuck Green. Though he guessed many of those involved were somehow related, Green said he didn’t know for certain what those connections are and police would likely continue discovering them throughout the investigation.

Green said he wasn’t aware Tuesday morning what initiated the investigation, which was done in cooperation with the Johnson County Joint Drug Task-force, which UI police are a member of. Investigators also worked with University Housing.

Though Iowa City police conducted their own drug bust on Lucas Street last night, officials say the two were unrelated.

Check back to dailyiowan.com throughout the day for more updates.