Authorities stumbled upon a key piece of evidence -- a hair in pliers in Scott Peterson's boat -- while reviewing evidence photographs in February, Modesto police Detective Al Brocchini testified.Brocchini acknowledged having called in a tip to a hot line operated by Scott Peterson's family and confirmed that he never attempted to contact Homer Maldonado or Vivian Mitchell. Both have said they saw Laci Peterson walking her dog in the La Loma neighborhood the morning of Dec. 24 -- after authorities contend that she was slain. Brocchini also said he passed information on Scott Peterson's spending habits to officials of Tradecorp, the Spain-based fertilizer firm that employed Peterson. The detective denied telling a close friend of the Petersons that he was "going to take Scott Peterson down."Police in early January tailed Scott Peterson to San Francisco Bay three times, Brocchini testified.