In a joint investigation, ProPublica Illinois’ Jodi Cohen and Jennifer Smith Richards of The Chicago Tribune teamed up to investigate  the use of seclusion rooms in Illinois’ public schools. In the process, they discovered that seclusion -- billed as a humane way to control misbehaving students -- was misused, overused and ended up being disproportionately inflicted on students with disabilities. Their reporting prompted not just outrage but swift action by the state’s lawmakers.    How did the journalists discover the abuses? How did they use social media and websites to track down potential sources? And how can local reporters follow their lead?