Previous tenants reported seeing mushrooms -- a clear sign of rot -- on a California balcony that collapsed, killing six college students, but the building's management did not close the structure off, according to lawsuits filed Thursday.

The 12 lawsuits filed in Alameda County by the families of five Irish students who died and seven people who were injured in the June collapse accuse the building manager, Greystar, the building owner, BlackRock, and the construction firm that built the balcony, Segue, of negligence. They suits seek unspecified damages.

"Our clients have authorized the filing of these claims with the hope that this litigation will bring to light the carelessness and negligence that caused this entirely avoidable tragedy that has produced so much pain and loss, both here and in Ireland," the law firm handling the suits, Walkup, Melodia, Kelly & Schoenberger, said in a statement.

Segue used cheaper materials to construct the balcony, making it more susceptible to water damage, and left it exposed to rain during construction in 2005, the lawsuit says. A city investigation following the collapse revealed wooden supporting beams on the balcony were rotted through from water damage.

A call after hours to Segue was not immediately returned. An email to Greystar was also not immediately returned.

BlackRock spokesman Brian Beades said the company had not reviewed the lawsuit, and might have comment later.

The balcony gave way during a birthday party, tossing the six who died and another seven young people 50 feet down to the street below.

The Alameda County district attorney has been conducting an investigation to determine if criminal charges are warranted.

The president of Ireland met with Berkeley's mayor and public safety workers last month to thank them for helping after the balcony collapsed.