what I learned

A random home invasion, one in which criminals drive down a street and indiscriminately select a home based on appeal or assumed riches, may be widely feared by the public, but in police circles it's virtually unheard of. Any seasoned investigator will tell you that in 99 percent of cases there is a distinct motive, a reason - a tip about a safe bursting with cash, rumors of jewelry, thousands of dollars under the mattress, or top-of-the-line sports cars. However, in all these instances the motive is material benefit, and those willing to take part would ensure the home is empty. After all, those who steal possessions can expect six months or less in prison; murder, on the other hand, can land you in prison for life. 
"combination bias," which occurs when detective seek out information that confirms their existing beliefs about a case.
"believing" someone, especially in the initial stage of an interview, can be the ideal technique. "Sometimes getting people to talk is the best way," he says. "A lie told is better than nothing spoken, because lies can be disproven. When nothing is said, the investigation... suffers. And that all depends on the interviewee...