Hundreds of thousands of firearms stolen from the homes and vehicles of legal owners are flowing each year into underground markets, and the numbers are rising. Those weapons often end up in the hands of people prohibited from possessing guns. Many are later used to injure and kill. A yearlong investigation by The Trace and more than a dozen NBC TV stations identified more than 23,000 stolen firearms recovered by police between 2010 and 2016 — the vast majority connected with crimes. That tally, based on an analysis of police records from hundreds of jurisdictions, includes more than 1,500 carjackings and kidnappings, armed robberies at stores and banks, sexual assaults and murders, and other violent acts committed in cities from coast to coast.