Virginia Tech began draining its campus pond Monday as part of the Virginia State Police investigation of the April 16 campus shootings.

Once the Duck Pond is drained, state police will perform a grid search of the mucky bottom to look for any evidence connected to the shootings, said state police spokeswoman Corinne Gellar.

Witnesses have told state police they saw Virginia Tech gunman Seung-Hui Cho at the pond in between shootings at West Ambler Johnston dormitory and Norris Hall the morning of April 16.

State police approached the university about searching the pond about a week ago, said Tech spokesman Mark Owczarski.

The decision to drain the body of water was mutual, Geller said. It will allow state police to perform a more thorough check, and give the university an opportunity to make repairs that were needed.

Investigators aren't targeting any evidence in particular, Geller said, adding that police have followed up on hundreds of leads during their investigation.

"It's just part of the process of elimination," she said.

State police searched the Duck Pond after the shootings without draining it, but they didn't find anything, Geller said.

Owczarski said he did not know how long the pond would take to drain but said it will remain empty after investigators are done with their work so that the repairs can be done.

He said it has been 20 years since the pond, created in 1937 by the damming of a creek, has been repaired. Crews will reinforce walls, clean up sediment and trim trees while the pond is drained.

Owczarski did not know how long the work will take or what it will cost. He said the pond could remain drained for several weeks.